Two Essays on Haeckel
GA 30
I. Haeckel and His Opponents
Preface
[ 1 ] I am convinced that my work, The Philosophy of Freedom, published some five years ago, gives the outline of a world-conception which is in complete harmony with the stupendous results of the natural science of our time. I am also conscious that I did not intentionally bring about this harmony. My road was quite independent of that which natural science follows.
[ 2 ] From this independence of my own way of looking at things in regard to the province of knowledge that is dominant in our day, and from its simultaneous, complete agreement therewith, I believe myself entitled to draw my justification for presenting the position of that monumental representative of the scientific mode of thought, Ernst Haeckel, in the intellectual battle of our time.
[ 3 ] Doubtless there are to-day many who feel the need for clearing up matters with regard to natural science. This need can best be satisfied by penetrating deeply into the ideas of that seeker into Nature who has most unreservedly drawn the full conclusions of scientific premises. I desire to address myself in this little book, to those who share with me a like need in this respect.
Rudolf SteineR
Berlin, January, 1900.
[ 4 ] Goethe has given glorious expression, in his book upon Winkelmann, to the feeling which a man has when he contemplates his position within the world: “When the healthy nature of man works as a whole, when he feels himself in the world as in a great, beautiful, worthy, and valuable whole, when harmonious contentment yields him pure, free rapture, then would the universe, could it but feel itself, burst forth into rejoicing at having attained its goal, and admire the summit of its own becoming and being.”
From out of this feeling there arises the most important question that man can ask himself: how is his own becoming and being linked with that of the whole world? Schiller, in a letter to Goethe of 23rd August, 1794, admirably characterises the road by which Goethe sought to come to a knowledge of human nature. “From the simple organism you ascend step by step to the more complex, in order finally to build up the most complex of all, man, genetically from the materials of the entire structure of nature.” Now this road of Goethe's is also that which natural science has been following for the last forty years, in order to solve “the question of questions for humanity.” Huxley sees the problem to be the determination of the position which “man occupies in nature, and his relation to the totality of things.” It is the great merit of Charles Darwin to have created a new scientific basis for reflection upon this question. The facts which he brought forward in 1859 in his work, The Origin of Species, and the principles which he there developed, gave to natural research the possibility of showing, in its own way, how well founded was Goethe's conviction that Nature, “after a thousand animal types, forms a being that contains them all—man.”
To-day we look back upon forty years of scientific development, which stand under the influence of Charles Darwin's line of thought. Rightly could Ernst Haeckel say in his book, On our Present Knowledge of Man's Origin, which reproduces an address delivered by him at the Fourth International Congress of Zoologists in Cambridge on 26th August, 1898: “Forty years of Darwinism! What a huge progress in our knowledge of Nature! And what a revolution in our weightiest views, not only in the more closely affected departments, but also in that of anthropology, and equally in all the so-called psychological sciences.”
Goethe, from his profound insight into Nature, foresaw to its full extent this revolution and its significance for the progress of man's intellectual culture. We see this particularly clearly from a conversation which he had with Soret on 2nd August, 1830. At that time the news of the beginning of the Revolution of July reached Weimar and caused general excitement. When Soret visited Goethe, he was received with the words: “Now, what do you think of this great event? The volcano has burst into eruption; all is in flames, and it is no longer a conference behind closed doors!” Soret naturally could only believe that Goethe was speaking of the July Revolution, and replied that under the known conditions nothing else could be expected than that it would end with the expulsion of the Royal family. But Goethe had something quite different in his mind. “1 am not talking of those people at all; I am concerned with quite other things. I am speaking of the conflict, so momentous for science, between Cuvier and Geoffroy de Saint-Hilaire that has come to a public outbreak in the Academy.” The conflict concerned the question whether each species in which organic nature finds expression possesses a distinct architectural plan of its own, or whether there is one plan common to them all. Goethe had already settled this question for himself forty years earlier. His eager study of the plant and animal worlds had made him an opponent of the Linnæan view, that we “count as many species as different forms were created in the beginning (in principio).” Anyone holding such an opinion can only strive to discover what are the plans upon which the separate species are organised. He will seek above all carefully to distinguish these separate forms.
Goethe followed another road. “That which Linnaeus strove forcibly to hold apart was bound, according to the innermost need of my being, to strive after reunion.” Thus there grew up in him the view which, in 1796, in the Lectures upon the three first chapters of A General Introduction to Comparative Anatomy, he summed up in the sentence: “This, then, we have gained, that we can unhesitatingly maintain that all complete organic natures—among which we see fishes, amphibia, birds, mammals, and, as the head of the last, man—have all been shaped according to one original type, which only inclines more or less to this side or the other in its constant parts, and yet daily develops and transforms itself by reproduction.” The basic type, to which all the manifold plant-forms may be traced back, had already been described by Goethe in 1790 in his Attempt to Explain the Metamorphosis of Plants. This way of regarding things, by which Goethe endeavoured to recognise the laws of living nature, is exactly similar to that which he demands for the inorganic world in his essay, written in 1793, Experiment as Mediator between Object and Subject: “Nothing happens in Nature which is not in some connection with the whole, and if experiences only appear to us as isolated, if we can only regard experiments as isolated facts, that does not imply that they actually are isolated; it is only the question: How shall we find the connection of these phenomena, these occurrences?” Species also appear to us only in isolation. Goethe seeks for their connection. Hence it clearly appears that Goethe's effort was directed to apply the same mode of explanation to the study of living beings as has led to the goal in that of inorganic nature.1I have characterised the contrast that exists between Goethe's and Kant's world-conceptions, in the Introductions to my edition of Goethe's Scientific Writings (in Kürschner, Deutsche National-Literatur) and in my book, Goethe's Conception of the World (p. 37 et seq.). It shows itself also in the attitude of the two personalities towards the explanation of organic nature. Goethe seeks for this explanation along the road which modern science has also trodden. Kant holds such an explanation to be impossible. Only one who penetrates deeply into the nature of Goethe's view of the world can acquire a correct judgment as to its position in regard to the Kantian philosophy. Goethe's own testimony is not conclusive, because he never devoted himself to a closer study of Kant. “The portal (of the Critique of Pure Reason) it was that pleased me, into the labyrinth itself I could not adventure: now it was my poetic gift that hindered me, now my commonsense, and I nowhere found myself any the better.” Single passages in Kant's Critique of Judgment pleased him, because he so interpreted their meaning that they agreed with his own view of the world. It is, therefore, only too easily understood why his conversations with followers of Kant appear somewhat peculiar. “They certainly listened to me, but could give me no answer, nor in any way help me on. More than once it happened to me, that one or the other confessed with smiling admiration: it may be something analogous to the Kantian mode of conception, but a rather strange one.” Karl Vorländer, in his essay Goethe's Verhältnis zu Kant in seiner historischen Entwickelung (Kantstudien, i., ii.), has judged this relationship according to the actual words of Goethe's own testimony, and has reproached me with the fact that my conception thereof is “in contradiction with the clear testimony of Goethe himself,” and, at the very least, “strongly one-sided.” I would have left this objection unanswered, because I saw from the explanations of Herr Karl Vorländer that they proceed from a man who finds it quite impossible to understand a mode of thinking which is strange to him; however, it still seemed to me needful not to leave without answer a remark which he couples thereto. Herr Vorländer belongs to those men who regard their own opinion as absolutely right, and therefore as proceeding from the highest possible insight, and who therefore stamp every other view as a product of ignorance. Because I think otherwise about Kant than he does, he gives me the sage advice to study certain portions of Kant's works. Such a mode of criticising other people's opinions cannot be too strongly repudiated. Who gives anyone the right, not to criticise me for an opinion differing from his own, but to schoolmaster me? I have therefore told Herr Karl Vorländer my opinion as to his school-mastering in the fourth volume of my edition of Goethe's Scientific Writings. Thereupon, in the third volume of Kantstudien, he has discussed my book, Goethe's Conception of the World, in a fashion which not only far surpasses in point of form what he had previously said against me, but which is also full of objective untruths. Thus he speaks of an “isolated and embittered opposition “in which I find myself against the whole of modern philosophy (naturally exclusive of Nietzsche) and science. There at once one has three objective untruths. Anyone who reads my writings—and whoever, like Herr Vorländer, pronounces judgment upon me, should at the least read them—will perceive that I do indeed criticise technically particular views of modern science and endeavour to deepen others philosophically; but that to talk of an embittered opposition is simply absurd. In my Philosophie der Freiheit I have expressed my conviction to the effect that in my views is given the philosophical completion of the structure which “Darwin and Haeckel have erected for Natural Science” (p. 186). That I am the one who has sharply emphasised the fundamental deficiency in the world of Nietzsche's ideas is indeed known to the Frenchman Henri Lichtenberger, who observes in his book La Philosophie de Nietzsche: “R. Steiner is the author of Truth and Science and The Philosophy of Freedom. In the latter work he completes Nietzsche's theory on an important point.” He emphasises the point which I have shown that Nietzsche's Superman is not that which he ought to be. The German philosopher, Karl Vorländer, has either not read my writings, and none the less passes judgment upon me; or else he has done so, and still writes the above and other similar objective untruths. I leave it to the judgment of the competent public to decide whether his contribution, which was found worthy of acceptance in a serious philosophical review, is a proof of his complete lack of judgment or a dubious contribution to the morality of German scholarship.
How far he had run ahead of his time with such conceptions becomes apparent when one reflects that at the same time when Goethe published his Metamorphosis, Kant sought to prove scientifically, in his Critique of Judgment, the impossibility of an explanation of the living according to the same principles as hold for the lifeless. He maintained: “It is quite certain that we cannot even adequately learn to know, far less explain to ourselves, the organised beings and their inner possibility according to purely mechanical principles of nature; and, indeed, it is so certain that we can boldly say it is senseless for man even to conceive such a purpose, or to hope that sometime perhaps a Newton may arise who will make comprehensible the production of a blade of grass according to natural laws which no purpose has ordered; rather one must simply and flatly deny any such insight to man.” Haeckel repudiates this thought with the words: “Now, however, this impossible Newton really appeared seventy years later in Darwin, and, as a matter of fact, solved the problem whose solution Kant had declared to be absolutely unthinkable!”
That the revolution in scientific views brought about by Darwinism must take place, Goethe knew full well, for it corresponds with his own way of conceiving things. In the view which Geoffroy de Saint-Hilaire defended against Cuvier, that all organic forms carry in them a “general plan modified only here and there,” he recognised his own again. Therefore he could say to Soret: “Now, however, Geoffroy de Saint-Hilaire is decidedly on our side, and with him all his important disciples and followers in France. This event is for me of quite extraordinary value, and I rejoice rightly over the general victory gained at length by a cause to which I have devoted my life, and which is most especially my very own.” Of still greater value for Goethe's view of Nature are, however, the discoveries of Darwin. Goethe's view of Nature is related to Darwinism in a way similar to that in which the insights of Copernicus and Kepler into the structure and movements of the planetary system are related to the discovery by Newton of the law of the universal attraction of all heavenly bodies. This law reveals the scientific causes, why the planets move in the manner which Copernicus and Kepler had described. And Darwin found the natural causes, why the common original type of all organic beings, which Goethe assumed, makes its appearance in the various species.
[ 5 ] The doubt as to the view that there underlies each distinct organic species a special plan of organisation, unchangeable for all time, took firm hold upon Darwin upon a journey which he undertook to South America and Australia in the summer of 1831 as naturalist on the ship Beagle. As to how his thought ripened, we get an idea in reaching such communications from him as the following: “When, during the voyage of the Beagle, I visited the Galapagos Archipelago, which lies in the Pacific Ocean some five hundred English miles from the South American coast, I saw myself surrounded by peculiar kinds of birds, reptiles, and snakes, which exist nowhere else in the world. Yet they almost all bore upon them an American character. In the song of the mocking thrush, in the sharp cry of the carrion hawk, in the great chandelier-like Opuntico, I clearly perceived the neighbourhood of America; and yet these islands were separated from the mainland by so many miles, and differed widely from it in their geological constitution and their climate. Yet more surprising was the fact that most of the inhabitants of each separate island of this small archipelago were specifically different, although closely related to one another. I often asked myself, then, how these peculiar animals and men had originated. The simplest answer seemed to be that the inhabitants of the different islands descend from one another, and in the course of their descent had undergone modifications, and that all the inhabitants of the archipelago had descended from those of the nearest mainland, viz., America, from which naturally the colonisation would proceed. But it long remained for me an unintelligible problem: how the necessary degree of modification could have been attained.”
As to this “how,” it was the numerous breeding experiments which he tried, after his return home, with pigeons, fowls, dogs, rabbits, and garden plants that enlightened Darwin. He saw from them in how high a degree there lies in organic forms the possibility of continually modifying themselves in the course of their reproduction. It is possible, by creating artificial conditions, to obtain from a given form after a few generations new kinds, which differ much more from each other than do those in Nature, whose difference is regarded as so great that one inclines to ascribe to each a special underlying plan of organisation. As is well known, the breeder utilises this variability of kinds to bring about the development of such forms of domesticated organisms as correspond with his intentions. He endeavours to create the conditions which guide the variation in a direction answering his purpose. If he seeks to breed a kind of sheep with specially fine wool, he seeks out among his flock those individuals which have the finest wool. These he allows to breed. From among their descendants he again selects for further breeding those which have the finest wool. If this is carried on through a series of generations, a species of sheep is obtained which differs materially from its ancestors in the formation of its wool. The same thing can be done with other characteristics of living creatures. From these facts two things become obvious: that organic forms have a tendency to vary, and that they pass on the acquired modifications to their descendants. Owing to this first property of living creatures, the breeder is able to develop in his species certain characteristics that answer his purposes; owing to the second, these new characteristics are handed on from one generation to the next.
[ 6 ] The thought now lies close at hand, that in Nature also, left to itself, the forms continually vary. And the great power of variation of domesticated organisms does not force us to assume that this property of organic forms is confined within certain limits. We may rather presuppose that in the lapse of vast time-periods a certain form transforms itself into a totally different one, which in its formation diverges from the former to the utmost extent imaginable. The most natural inference then, is this, that the organic species have not arisen independently, each according to a special plan of structure, alongside each other; but that in course of time they have evolved the one from the other. This idea gains support from the views at which Lyell arrived in the history of the earth's development, and which he first published in 1830 in his Principles of Geology. The older geological views, according to which the formation of the earth was supposed to have been accomplished in a series of violent catastrophes, were thereby superseded. Through this doctrine of catastrophes it was sought to explain the results to which the investigation of the earth's solid crust had led. The different strata of the earth's crust, and the fossilised organic creatures contained in them, are of course the vestiges of what once took place on the earth's surface.
The followers of the doctrine of violent transformations believed that the development of the earth had been accomplished in successive periods, definitely distinguished from one another. At the end of such a period there occurred a catastrophe. Everything living was destroyed, and its remains preserved in an earth-stratum. On the top of what had been destroyed there arose a completely new world, which must be created afresh. In the place of this doctrine of catastrophes, Lyell set up the view that the crust of the earth has been gradually moulded in the course of very long periods of time, by the same processes which still in our time are going on every day on the earth's surface. It has been the action of the rivers carrying mud away from one spot and depositing it on another; the work of the glaciers, which grind away rocks and stones, forward blocks of stone, and analogous processes, which, in their steady, slow working have given to the earth's surface its present configuration. This view necessarily draws after it the further conclusion that the present-day forms of plants and animals also have gradually developed themselves out of those whose remains are preserved for us in fossils. Now, it results from the processes of artificial breeding that one form can really transform itself into another. There remains only the question, by what means are those conditions for this transformation, which the breeder brings about by artificial means, created in Nature itself?
[ 7 ] In artificial breeding human intelligence chooses the conditions so that the new forms coming into existence answer to the purposes which the breeder is following out. Now, the organic forms living in Nature are in general purposefully adapted to the conditions under which they live. A mere glance into Nature will teach one the truth of this fact. Plant and animal species are so constructed that they can maintain and reproduce themselves in the conditions under which they live.
[ 8 ] It is just this purposeful arrangement which has given rise to the supposition that organic forms cannot be explained in the same way as the facts of inorganic Nature. Kant observes in his Critique of Judgment: “The analogy of the forms, in so far as they seem to be produced in accordance with a common basic plan, despite all differences, strengthens the presumption of a real relationship between them in their generation from a common mother through an approach, step by step, of one animal species to another. ... Here, therefore, it is open to the archaeologist of Nature to cause to arise that great family of creatures (for one would be forced to conceive them thus if the thoroughgoing connected relationship spoken of is to hold good) from the traces left over of her older revolutions, according to all their known and supposed mechanisms. But he must equally for that purpose ascribe to this common mother an organisation purposely fitted to all these creatures, for otherwise the purposive form of the products of the plant and animal kingdoms is unthinkable as to its possibility.”
[ 9 ] If we would explain organic forms after the same manner in which natural science deals with inorganic phenomena, we must demonstrate that the particular arrangement of the organisms—devoid of a purposeful object—comes into being by reason of what is practically natural necessity, even as one elastic ball after having been struck by another is fulfilling a law as it rolls along. This requirement has its fulfilment in Darwin's teachings regarding natural selection. Even in Nature organic forms must, in accordance with their capacity for assimilating modifications which have been brought about by artificial breeding, become transformed. Should there be nothing available for directly bringing about the change, so that none but the forms aimed at should come into existence, there will be, regardless of choice, useless, or less useful, forms called into being. Now, Nature is extremely wasteful in the bringing forth of her germs. So many germs are, indeed, produced upon our earth, that were they all to attain to development we should soon be able to fill several worlds with them.
This great number of germs is confronted with but a comparatively small amount of food and space, the result of this being a universal struggle for existence among organic beings. Only the fit survive and fructify; the unfit have to go under. The fittest, however, will be those who have adapted themselves in the best possible way to the surrounding conditions of life. The absolutely unintentional, and yet—from natural causes—necessary, struggle for existence brings in its train the same results as are attained by the intelligence of the breeder with his cultivated organisms: he creates purposeful (useful) organic forms. This, broadly sketched, is the meaning of Darwin's theory of natural selection in the struggle for existence; or, otherwise, the “selective theory.” By this theory, that which Kant held to be impossible is reached: the thinking out in all its possibilities of a predetermined form in the animal and vegetable kingdom, without assuming the Universal Mother to be dowered with an organism directly productive of all these creatures.
[ 10 ] As Newton by pointing out the general attraction of the heavenly bodies showed why they moved in the set courses determined by Copernicus and Kepler, so did it now become possible to explain with the help of the theory of selection how in Nature the evolution of the living thing takes place, the course of which Goethe, in his Metamorphosis of Plants, has observed: “We can, however, say this, namely, that proceeding from a relationship that is hardly distinguishable between animal and plant, creatures do little by little evolve, carrying on their development in opposite directions—the plant finally reaching its maturity in the form of the tree, and the animal finding its culminating glory in man's freedom and activity.”
Goethe has said of his ancestors: “I shall not rest until I have found a pregnant point from which many deductions may be made; or, rather, one that will forcibly bestow upon me the overflow of its own abundance.” The theory of selection became for Ernst Haeckel the point from which he was able to deduce a conception of the universe entirely in accordance with natural science.
[ 11 ] At the beginning of the last century Jean Lamarck also maintained the view that, at a certain moment in the earth's development, a most simple organic something developed itself, by spontaneous generation, out of the mechanical, physical, and chemical processes. These simplest organisms then produced more perfect ones, and these again others more highly organised, right up to man. “One might therefore quite rightly name this part of the theory of evolution, which asserts the common origin of all plant and animal species from the simplest common root-forms, in honour of its most deserving founder, Lamarckianism” (Haeckel, Natural History of Creation). Haeckel has given in grandiose style an explanation of Lamarckianism by means of Darwinism.
[ 12 ] The key to this explanation Haeckel found by seeking out the evidences in the individual development of the higher organisms—in their ontogeny—showing that they really originated from lower forms of life. When one follows out the form-development of one of the higher organisms from the earliest germ up to its fully developed condition, the different stages are found to present configurations corresponding to the forms of lower organisms.2Fundamental Biogenetic Law. Haeckel has proved in a series of works the general validity and far-reaching significance of the fundamental biogenetic law. The most important explanations and proofs will be found in his Biology of the Corals (1872) and in his Studies in the Gastrula Theory (1873–84). Since then other zoologists have extended and confirmed this doctrine. In his latest work, Die Welträtsel (1899), Haeckel is able to say of it (p. 72): “Although this doctrine was at the outset almost generally rejected, and for some ten years fiercely combated by numerous authorities, yet, at the present time (for about fifteen years past), it has been accepted by all well-informed specialists in the subject.” At the outset of his individual existence man and every other animal is a simple cell. This cell divides itself, and from it arises a germinal vesicle consisting of many cells. From that develops the so-called “cup-germ,” the two-layered gastrula, which has the shape of a cup- or jug-like body. Now, the lower plant-animals (sponges, polyps, and so on) remain throughout their entire existence on a level of development which is equivalent to this cup-germ. Haeckel remarks thereupon: “This fact is of extraordinary importance. For we see that man, and generally every vertebrate, runs rapidly, in passing, through a two-leaved stage of formation, which in these lowest plant-animals is maintained throughout life” (Anthropogenesis). Such a parallelism between the developmental stages of the higher organisms and the developed lower forms may be followed out through the entire evolutionary history. Haeckel clothes this fact in the words: “The brief ontogenesis or development of the individual is a rapid and abbreviated repetition, a condensed recapitulation of the prolonged phylogenesis or development of the species.” This sentence gives expression to the so-called fundamental biogenetic law. Why then do the higher organisms in the course of their development come to forms which resemble lower ones? The natural explanation is that the former have developed themselves out of the latter; that therefore every organism in its individual development shows us one after another the forms which have clung to it as heirlooms from its lower ancestors.
[ 13 ] The simplest organism that once upon a time formed itself on earth, transforms itself in the course of reproduction into new forms. Of these, the best adapted in the struggle for existence survive, and transmit their peculiarities to their descendants. All the formations and qualities which an organism exhibits at the present time have arisen in the lapse of enormous time-periods by adaptation and inheritance. Heredity and adaptation are thus the causes of the world of organic forms.
[ 14 ] Thus, by investigating the relationship of individual developmental history (ontogeny) to the history of the race (phylogeny), Haeckel has given the scientific explanation of the manifold organic forms.3In his recently published book, Die Welträtsel, Gemeinverständliche Studien über Monistische Philosophie (Bonn, Emil Strauss, 1899), Haeckel has given without reserve the” further development, proof, and completion of the convictions” which throughout a full generation he has represented. To anyone who has absorbed the scientific knowledge of our time, this work must appear as one of the most important manifestos of the end of the nineteenth century. It contains in ripened form a complete analytical discussion of the relations of modern science with philosophical thinking from the mind of the most original, far-sighted investigator of our time. As a natural philosopher he has satisfied the human demand for knowledge, which Schiller had derived from observation of Goethe's mind; he ascended from the simple organisations step by step to the more complicated, to finally build up genetically the most complex of all, man, from the materials of the whole structure of Nature. He has set forth his view in several grandly designed works—in his General Morphology (1866), in his Natural History of Creation (1868), in his Anthropogenesis (1874)—in which he “undertook the first and hitherto the only attempt to establish critically in detail the zoological family-tree of man, and to discuss at length the entire animal ancestry of our race.” To these works there has been further added in recent years his three-volumed Systematic Phylogeny.
[ 15 ] It is characteristic of Haeckel's deeply philosophical nature that, after the appearance of Darwin's Origin of Species, he at once recognised the full significance for man's entire conception of the Universe, of the principles therein established; and it speaks much for his philosophical enthusiasm that he boldly and tirelessly combated all the prejudices which arose against the acceptance of the new truth by the creed of modern thought. The necessity that all modern scientific thinking should reckon with Darwinism was expounded by Haeckel at the fiftieth meeting of German scientists and doctors on the 22nd September, 1877, in his address, The Present Theory of Evolution in Relation to Science as a Whole. He delivered a widely-embracing Confession of Faith of a Man of Science on the 9th October, 1892, in Altenburg at the seventy-fifth anniversary of the Society for Natural Science of the Osterland. (This address was printed under the title, Monism as a link between Religion and Science, Bonn, 1892.) What has been yielded by the remodelled doctrine of evolution and our present scientific knowledge towards the answering of the “question of questions,” he has recently expounded in its broad lines in the address mentioned above, On our Present Knowledge as to the Origin of Man. Herein Haeckel handles afresh the conclusion, which follows as a matter of course from Darwinism for every logical thinker, that man has developed out of the lower vertebrates, and further, more immediately from true apes.
It has been, however, this necessary conclusion which has summoned to battle all the old prejudices of theologians, philosophers, and all who are under their spell. Doubtless, people would have accepted the emergence of the single animal and plant forms from one another if only this assumption had not carried with it at once the recognition of the animal descent of man. “It remains,” as Haeckel emphasised in his Natural History of Creation, “an instructive fact that this recognition—after the appearance of the first Darwinian work—was in no sense general, that on the contrary numerous critics of the first Darwinian book (and among them very famous names) declared themselves in complete agreement with Darwinism, but entirely rejected its application to man.” With a certain appearance of justice, people relied in so doing on Darwin's book itself, in which no word is said of this application. Because he drew this conclusion unreservedly, Haeckel was reproached with being “more Darwinian than Darwin.” True, that held good only till the year 1871, in which appeared Darwin's work, The Descent of Man and Sexual Selection, in which Darwin himself maintained that inference with great boldness and clearness.
[ 16 ] It was rightly recognised that with this conclusion must fall a conception belonging to the most treasured among the collection of older human prejudices: the conception that the “soul of man” is a special being all to itself, having quite another, a different, “higher origin” from all other things in Nature. The doctrine of descent must naturally lead to the view that man's soul-activities are only a special form of those physiological functions which are found in his vertebrate ancestors, and that these activities have evolved themselves with the same necessity from the mental activities of the animals, as the brain of man, which is the material condition of his intellect, has evolved out of the vertebrate brain.
[ 17 ] It was not only the men with old conceptions of faith nurtured in the various ecclesiastical religions who rebelled against the new confession, but also all those who had indeed apparently freed themselves from these conceptions of faith, but whose minds nevertheless still thought in the sense of these conceptions. In what follows the proof will be given that to this latter class of minds belong a series of philosophers and scientific scholars of high standing who have combated Haeckel, and who still remain opponents of the views he advocated. To these ally themselves also those who are entirely lacking in the power of drawing the necessary logical conclusions from a series of facts lying before them. I wish here to describe the objections which Haeckel had to combat.
II
[ 18 ] A bright light is thrown upon the relationship of man to the higher vertebrates, by the truth which Huxley, in 1863, expressed in his volume on Man's Place in Nature, and other Anthropological Essays: “Thus whatever system of organs be studied, the comparison of their modifications in the ape series leads to one and the same result—that the structural differences which separate man from the gorilla and the chimpanzee are not so great as those which separate the gorilla from the lower apes” (see Man and the Lower Animals, p. 144). With the help of this fact it is possible to establish man's animal line of ancestry in the sense of the Darwinian doctrine of descent. Man has common ancestors with the apes in some species of apes that have died out. By a corresponding utilisation of the knowledge which comparative anatomy and physiology, individual developmental history, and palaeontology supply, Haeckel has followed the animal ancestors of man lying still more remotely in the past, through the semi-apes, the marsupials, the earliest fishes, right up to the very earliest animals consisting only of a single cell. He is fully entitled to ask: “Are the phenomena of the individual development of man in any way less wonderful than the palaeontological development from lower organisms? Why should not man have evolved in the course of enormous periods of time from unicellular original forms, since every individual runs through this same development from the cell to the fully developed organism?”
[ 19 ] But it is also by no means easy for the human mind to construct for itself conceptions in accordance with Nature as regards the unfoldment of the single organism from the germ up to the developed condition. We can see this from the ideas which a scientist like Albrecht von Haller (1708-1777) and a philosopher like Leibnitz (1646-1716) formed about this development. Haller maintained the view that the germ of an organism already contains in miniature, but fully and completely formed in advance, all the parts which make their appearance during its development. Thus, development is taken to be not the formation of something new in what is already present, but the unfolding of something that was already there but invisible to the eye because of its minuteness. But if this view were correct, then in the first germ of an animal or vegetable form all following generations must be already contained like boxes one inside the other. And Haller actually drew this conclusion. He assumed that in the first human germ of our root-mother, Eve, the entire human race was already present in miniature. And even Leibnitz also can only imagine the development of men as an unfoldment of what already exists: “So I should opine that the souls, which some day will be human souls, were already there in germ, like those of other species, that they existed in man's ancestors up to Adam, therefore from the beginning of things, always in the form of organised bodies.”
[ 20 ] The human understanding has a tendency to imagine to itself that anything coming into existence was somehow already there, in some form or other, before its manifestation. The entire organism is supposed to be already hidden in the germ; the distinct organic classes, orders, families, species, and kinds are supposed to have existed as the thoughts of a creator before they actually came into existence. Now, however, the idea of evolution demands that we should conceive the arising of something new, of something later, from out of something already present, of something earlier. We are called upon to understand that which has become, out of the becoming. That we cannot do, if we regard all that has become as something which has always been there.
[ 21 ] How great the prejudices are that the idea of evolution had to face was clearly shown by the reception which Caspar Friedrich Wolff's Theoria Generationis, which appeared in 1759, met with among the men of science who accepted Haller's views. It was demonstrated in this book that in the human ovum not even a trace of the form of the developed organism is present, but that its development consists in a series of new formations. Wolff defended the idea of a real evolution, an epigenesis, a becoming from what is not present, as against the view of seeming evolution. Haeckel says of Wolff's book that it “belongs, in spite of its small size and awkward language, to the most valuable writings in the whole field of biological literature. ...” Nevertheless, this remarkable book had at first no success whatever. Although scientific studies, as a result of the stimulus imparted by Linnaeus, flourished mightily at that time, although botanists and zoologists were soon counted no longer by dozens but by hundreds, yet no one troubled himself about Wolff's Theory of Generation. The few, however, who had read it, held it to be fundamentally wrong, and especially Haller. Although Wolff proved by the most accurate observations the truth of epigenesis, and disproved the current hypotheses of the preformation doctrine, nevertheless the “exact” physiologist Haller remained the most zealous follower of the latter and rejected the correct teaching of Wolff with his dictatorial edict: “There is no becoming” (Nulla est epigenesis!). With so much power did human thinking set itself against a view, of which Haeckel (in his Anthropogenesis) remarks: “To-day we can hardly any longer call this theory of epigenesis a theory, because we have fully convinced ourselves of the correctness of the fact, and can demonstrate it at any moment with the help of the microscope.”
[ 22 ] How deep-rooted is the prejudice against the idea of evolution can be seen at any moment by the objections which our philosophical contemporaries make against it. Otto Liebmann, who, in his Analysis of Reality and his Thoughts and Facts, has subjected the fundamental views of science to criticism, expresses himself in a remarkable manner about the conception of evolution. In face of the facts, he cannot deny the justice of the conception that higher organisms proceed from lower. He therefore endeavours to represent the range and importance of this conception for the higher need of explanation as being as small as possible. “Accepted, the theory of descent ... granted that it be complete, that the great genealogical register of Nature's organic beings lies open before us; and that, not as an hypothesis, but as historically proven fact, what should we then have? A gallery of ancestors, such as one finds also in princely castles; only not as a fragment, but as a completed whole.” This means that nothing of any consequence has been accomplished towards the real explanation, when one has shown how what appears later proceeds as a new formation from what preceded.
Now it is interesting to see how Liebmann's presuppositions lead him yet again to the assumption that what arises on the road of evolution was there already before its appearance. In the recently published second part of his Thoughts and Facts he maintains: “It is true that for us, to whom the world appears in the form of perception known as time, the seed is there before the plant; begetting and conception come before the animal that arises from them, and the development of the embryo into a full-grown creature is a process of time and drawn out in time to a certain length. In the timeless world-being, on the contrary, which neither becomes nor passes away, but is once and for all, maintaining itself unchangeably amid the stream of happenings, and for which no future, no past, but only an eternal present exists, this before and after, this earlier and later, falls away entirely. ... That which unrolls itself for us in the course of time as the slower or more rapidly passing succession of a series of phases of development, is in the omnipresent, permanent world-being a fixed law, neither coming into existence nor passing away.”
The connection of such philosophical conceptions with the ideas of the various religious doctrines as to the creation may be easily seen. That purposefully devised beings arise in Nature, without there being some fundamental activity or power which infuses that purposefulness into the beings in question, is something that neither these religious doctrines nor such philosophical thinkers as Liebmann will admit. The view that accords with Nature follows out the course of what happens, and sees beings arise which have the quality of purposefulness, without this same purpose having been a co-determinant in their production. The purposefulness came about along with them; but the purpose did not co-operate in their becoming.4Those who would willingly cling in faith to the existence of purposes in Nature, are constantly emphasising the fact that Darwin's views do not by any means exclude the idea of purpose, but rather make full use thereof, inasmuch as they show how the linking of causes and effects of necessity by themselves lead to the arising of the purposeful. The important point, however, is not whether or no one admits the existence of purposeful formations in Nature, but whether one assumes or rejects the idea that the purpose, the goal, co-operates as a cause in the development of these formations. Anyone who makes this assumption defends teleology, or the doctrine of purpose. Whoever says, on the contrary, purpose is in no way whatever operative in the production of the organic world; living creatures come into existence according to necessary laws just as do inorganic phenomena, and purposefulness is only there because that which is not purposeful cannot maintain itself; it is not the cause of what happens, but its consequence: he makes confession of Darwinism. No heed is paid to this by anyone who asserts, like Otto Liebmann, “Charles Darwin is one of the greatest teleologists of the present day” (Thoughts and Facts, pt. i, p. 113). No, he is the greatest anti-teleologist, because he would show to such minds as Liebmann, if they understood him, that the purposeful can be explained without assuming the action of operative purposes. The religious mode of conception has recourse to the Creator, who has created the creatures purposefully according to his preconceived plan; Liebmann turns to a timeless world-being, but he still makes that which is purposeful be brought forth by the purpose. “The goal or the purpose is here not later, and also not earlier than the means; but the purpose helps it on in virtue of a timeless necessity.” (Thoughts and Facts, pt. ii, p. 268.) Liebmann is a good example of those philosophers who have apparently freed themselves from the conceptions of faith, but who still think altogether on the lines of such conceptions. They profess that their thoughts are determined purely by reasonable considerations, but none the less it is an innate theological prejudice which gives the direction to their thoughts.
[ 23 ] Reasoned reflection must therefore agree with Haeckel when he says: “Either organisms have naturally developed themselves, and in that case they must all originate from the simplest common ancestral forms—or that is not the case, the various species of organisms have arisen independently of one another, and in that case they can only have been created in a supernatural manner, by a miracle. Natural evolution or supernatural creation of species—we must choose between these two possibilities, for there is no third!” (Free Science and Free Teaching, p. 9.) What has been proffered by philosophers or scientists as such a third alternative against the doctrine of natural evolution shows itself, on closer examination, to be only a belief in creation which more or less veils or denies its origin.
[ 24 ] When we raise the question as to the origin of species in its most important form, in that which concerns the origin of man, there are only two answers possible. Either a consciousness endowed with reason is not present prior to its actual appearance in the world, but evolves as the outcome of the nervous system concentrated in the brain; or else an all-dominating world-reason exists before all other beings, and so shapes matter that in man its own image comes into being. Haeckel (in Monism as the Link between Religion and Science, p. 21) describes the becoming of the human mind as follows: “As our human body has slowly and step by step built itself up from a long series of vertebrate ancestors, so the same thing holds good of our soul: as a function of our brain it has developed itself step by step in interaction with that organ. What we term for short the ‘human soul’ is indeed only the sum-total of our feeling, willing, and thinking—the sum-total of physiological functions whose elementary organs consist of the microscopic ganglionic cells of our brain. Comparative anatomy and ontogeny show us how the marvellous structure of the latter, of our human soul-organ, has built itself upwards gradually in the course of millions of years out of the brain-forms of the higher and lower vertebrates; while comparative psychology shows us how, hand in hand therewith, the very soul itself—as a function of the brain—has evolved itself. The latter shows us also how a lower form of soul activity is already present in the lowest animals, in the unicellular protozoa, infusoria, and rhizopods. Every scientist who, like myself, has observed through long years the life-activity of these unicellular protista, is positively convinced that they also possess a soul; this ‘cell-soul,’ too, consists of a sum of feelings, representations, and volitions; the feeling, thinking, and willing of our human soul is only different therefrom in degree.”
The totality of human soul-activities, which find their highest expression in unitary self-consciousness, corresponds to the complex structure of the human brain,5Organs of Thought. Quite recently Paul Flechsig has succeeded in proving that in one portion of the human organs of thought, complicated structures are found which are not present in other mammalia. These obviously are the organs of those mental activities by which man is distinguished from the animal. just as simple feeling and willing do to the organisation of the protozoa. The progress of physiology, which we owe to investigators like Goltz, Münk, Wernicke, Edinger, Paul Flechsig, and others, enables us to-day to assign particular soul-manifestations to definite parts of the brain as their special functions. We recognise in four tracts of the grey matter of the cortex the mediators of four kinds of feeling: the sphere of bodily organic feeling in the meso-cranum lobule, that of smell in the frontal lobule, that of vision in the chief basal lobule, that of hearing in the temple lobule. The thinking which connects and orders the sensations has its apparatus between these four “sense-foci.” Haeckel links the following remark to the discussion of these latest physiological results: “The four thought-foci, distinguished by peculiar and highly complicated nerve-structure from the intervening sense-foci, are the true organs of thought, the only real tools of our mental life” (On our Present Knowledge as to the Origin of Man, P-15).
[ 25 ] Haeckel demands from the psychologists that they shall take such results as these into account in their explanations about the nature of the soul, and not build up a mere pseudo-science composed of a fantastic metaphysic, of one-sided, so-called inner observation of soul-events, uncritical comparison, misunderstood perceptions, incomplete experiences, speculative aberrations and religious dogmas. As against the reproach that is cast by this view at the old-fashioned psychology, we find in some philosophers and also in individual scientists the assertion that there cannot in any case be contained in the material processes of the brain that which we class together as mind and spirit; for the material processes in the areas of sense and thought are in no case representations, feelings, and thoughts, but only material phenomena. We cannot learn to know the real nature of thoughts and feelings through external observation, but only through inner experience, through purely mental self-observation. Gustav Bunge, for instance, in his address Vitalism and Mechanism, p. 12, explains: “In activity—therein lies the riddle of life. But we have not acquired the conception of activity from observation through the senses, but from self-observation, from the observation of willing as it comes into our consciousness, as it reveals itself to our inner sense.” Many thinkers see the mark of a philosophical mind in the ability to rise to the insight that it is a turning upside down of the right relation of things, to endeavour to understand mental processes from material ones.
[ 26 ] Such objections point to a misunderstanding of the view of the world which Haeckel represents. Anyone who has really been saturated with the spirit of this view will never seek to explore the laws of mental life by any other road than by inner experience, by self-observation. The opponents of the scientific mode of thought talk exactly as if its supporters sought to discover the truths of logic, ethics, aesthetics, and so forth, not by means of observing mental phenomena as such, but from the results of brain-anatomy. The caricature of the scientific world-conception thus created by such opponents for themselves is then termed materialism, and they are untiring in ever repeating afresh that this view must be unproductive, because it ignores the mental side of existence, or at least gives it a lower place at the expense of the material. Otto Liebmann, whom we may here cite once more, because his anti-scientific conceptions are typical of the mode of thought of certain philosophers and laymen, observes: “But granting, however, that natural science had attained its goal, it would then be in a position to show me accurately the physico-organic reasons why I hold that the assertion ‘twice two are four’ is true and assert it, and the other assertion ‘twice two are five’ is false and combat it, or why I must, just at this moment, write these very lines on paper the while I am entangled in the subjective belief that this happens because I will to write them down on account of their truth as assumed by me” (Thoughts and Facts, pt. ii, p. 294 et seq.). No scientific thinker will ever be of opinion that bodily-organic reasons can throw any light upon what, in the logical sense, is true or false. Mental connections can only be recognised from the side of the mental life. What is logically justified, must always be decided by logic; what is artistically perfect, by the aesthetic judgment. But it is an altogether different question to inquire: How does logical thinking, or the aesthetic judgment arise as a function of the brain? It is on this question only that comparative physiology and brain-anatomy have anything to say. And these show that the reasoning consciousness does not exist in isolation for itself, only utilising the human brain in order to express itself through it, as the piano-player plays on the piano; but that our mental powers are just as much functions of the form-elements of our brain, as “every force is a function of a material body” (Haeckel, Anthropogenesis, pt. ii, p. 853).
[ 27 ] The essence of Monism consists in the assumption that all occurrences in the world, from the simplest mechanical ones upwards to the highest human intellectual creations, evolve themselves naturally in the same sense, and that everything which is called in for the explanation of appearances, must be sought within that same world. Opposed to this view stands Dualism, which regards the pure operation of natural law as insufficient to explain appearances, and takes refuge in a reasoning being ruling over the appearances from above. Natural science, as has been shown, must reject this dualism.
[ 28 ] Now, however, it is urged from the side of philosophy that the means at the disposal of science are insufficient to establish a world-conception. From its own standpoint science was entirely right in explaining the whole world-process as a chain of causes and effects, in the sense of a purely mechanical conformity to law; but behind these laws, nevertheless, there is hidden the real cause, the universal world-reason, which only avails itself of mechanical means in order to realise higher, purposeful relations. Thus, for instance, Arthur Drews, who follows in the path of Eduard von Hartmann, observes: “Human works of art, too, are produced in a mechanical manner, that is when one looks only at the outward succession of single moments, without reflecting on the fact that after all there is hidden behind all this only the artist's thought; nevertheless one would rightly take that man for a fool who would perchance contend that the work was produced purely mechanically ... that which presents itself as the inevitable effect of a cause, on that lower standpoint which contents itself with merely gazing at the effects and thus contemplates the entire process as it were from behind, that very same thing reveals itself, when seen from the front, in every case as the intended goal of the means employed” (German Speculation since Kant, vol. ii, p. 287 et seq.). And Eduard von Hartmann himself remarks about the struggle for existence which renders it possible to explain living creatures naturally: “The struggle for existence, and therewith the whole of natural selection, is only the servant of the Idea, who is obliged to perform the lower services in its realisation, namely, the rough hewing and fitting of the stones that the master-builder has measured out and typically determined in advance according to their place in the great building. To proclaim this selection in the struggle for existence as the essentially adequate principle of explanation of the evolution of the organic kingdom, would be on a par with a day-labourer, who had worked with others in preparing the stones in the building of Cologne Cathedral, declaring himself to be the architect of that work of art” (Philosophy of the Unconscious, 10th ed., vol. iii, p. 403).
[ 29 ] If these conceptions were justified, it would be the task of philosophy to seek the artist behind the work of art. In fact, philosophers have tried the most various and diverse dualistic explanations to account for Cosmic processes. They have constructed in thought certain entities, supposed to hover behind the phenomena as the spirit of the artist rules behind the work of art.
[ 30 ] No scientific consideration would be able to rob man of the conviction that perceptible phenomena are guided by beings outside the world, if he could find within his own consciousness anything that pointed to such beings. What could anatomy and physiology accomplish with their declaration that soul-activities are functions of the brain, if observation of these activities yielded anything which could be regarded as a higher ground for an explanation? If the philosopher were able to show that a universal world-reason manifests itself in human reason, then all scientific results would be powerless to refute such knowledge.
[ 31 ] Now, however, the dualistic world-conception is disproved by nothing more effectively than by the consideration of the human mind. When I want to explain an external occurrence—for instance, the motion of an elastic ball which has been struck by another, I cannot stop short at the mere observation, but must seek the law which determines the direction of motion and velocity of the one ball from the direction and velocity of the other. Mere observation cannot furnish me with such a law, but only the linking together in thought of what happens. Man, therefore, draws from his mind the means of explaining that which presents itself to him through observation. He must pass beyond the mere observation, if he wants to comprehend it. Observation and thought are the two sources of our knowledge about things; and that holds good for all things and happenings, except only for the thinking consciousness itself. To that we cannot add by any explanation anything that does not lie already in the observation itself. It yields us the laws for all other things; it yields us at the same time its own laws also. If we want to demonstrate the correctness of a natural law, we accomplish this by distinguishing, arranging observations and perceptions, and drawing conclusions—that is, we form conceptions and ideas about the experiences in question with the help of thinking. As to the correctness of the thinking, thought itself alone decides. It is thus thought which, in regard to all that happens in the world, carries us beyond mere observation, though it does not carry us beyond itself.
[ 32 ] This fact is incompatible with the dualistic world-conception. The point which the supporters of this conception so often emphasise, namely, that the manifestations of the thinking consciousness are accessible to us through the inner sense of introspection, while we only comprehend physical and chemical happenings when we bring into the appropriate connections the facts of observation through logical, mathematical combination, and so on; in other words, through the results of the psychological domain: this fact is the very thing which they should never admit. For let us for once draw the right conclusion from the knowledge that observation transforms itself into self-observation when we ascend from the scientific into the psychological domain.
If a universal world-reason underlay the phenomena of nature, or some other spiritual primordial being (for instance, Schopenhauer's will or von Hartmann's unconscious spirit), then it follows that the human thinking spirit must also be created by this world-being. An agreement of the conceptions and ideas which the mind of man forms from phenomena, with the actual laws proper to these occurrences, would only be possible if the ideal world-artist called forth in the human soul the laws according to which he had previously created the entire world. But then man could only know his own mental activity through observation of the root-being by whom he is shaped, and not through self-observation. Indeed, there could be no self-observation, but only observation of the intentions and purposes of the primordial being. Mathematics and logic, for example, ought not to be developed by means of man's investigating the inner, proper nature of mental connections, but by his deducing these psychological truths from the intentions and purposes of the eternal world-reason. If human understanding were only the reflection of an eternal mind, then it could never possibly ascertain its own laws through self-observation, but must needs explain them from out of the eternal reason. But whenever such an explanation has been attempted, it is simply human reason which has been transferred to the world outside. When the mystic believes that he rises to the contemplation of God by sinking down into his own inner being, in reality he merely sees his own spirit, which he makes into God; and when Eduard von Hartmann speaks of ideas which utilise the laws of Nature as their hodmen-helpers in order to shape the building of the world, these ideas are only his own, by means of which he explains the world. Because observation of the manifestations of mind is self-observation, therefore it follows that it is man's own spirit which expresses itself in the mind, and not any external reason.
[ 33 ] The monistic doctrine of evolution, however, is in complete agreement with the fact of self-observation. If the human soul has evolved itself slowly and step by step along with the organs of the soul out of lower conditions, then it is self-evident that we can explain its development from below scientifically, though we can discover the inner nature of that which emerges from the complex structure of the human brain only from the contemplation of this very nature itself. Had spirit been always present in a form resembling the human, and had it at last created its likeness in man alone, then we ought to be able to deduce the human spirit from the All-spirit; but if man's spirit has arisen as a new formation in the course of natural evolution, then we can understand its origin by following out its line of ancestry; we learn to know the stage at which it has at last arrived when we contemplate that spirit itself.
[ 34 ] A philosophy that understands itself, and turns its attention to an unprejudiced contemplation of the human spirit, thus yields a further proof of the correctness of the monistic world-conception. It is, however, quite incompatible with a dualistic natural science. (The further development and detailed proof of a monistic philosophy, the basic ideas of which I can only indicate here, I have given in my =The Philosophy of Freedom, Berlin, 1894, Verlag Emil Felber.)
[ 35 ] For one who understands aright the monistic world-conception, all the objections urged against it from the side of ethics lose all significance. Haeckel has repeatedly pointed out the injustice of such objections, and also called attention to the fact that the assertion that scientific monism must needs lead to ethical materialism, either rests upon a complete misunderstanding of the former, or else aims at nothing more than casting suspicion upon it.
[ 36 ] Naturally monism regards human conduct only as a part of the general happenings of the world.6Human and Animal Psychology. The merit of having proved that there is no real contrast between the soul of man and that of animals, but that the mental activities of man are linked to those of animals as a higher form thereof in a perfectly natural chain of development, belongs to George Romanes, who, in a comprehensive work, Mental Evolution in Animals (vol. i) and Mental Evolution in Man and the Origin of Human Faculties (vol. ii), has shown, “that the psychological barrier between animal and man has been surmounted.” It makes that conduct just as little dependent upon a so-called higher moral world-order, as it makes the happenings in Nature dependent upon a supernatural order. “The mechanical or monistic philosophy maintains that, everywhere in the phenomena of human life, as in those of the rest of nature, fixed and unalterable laws rule, that everywhere there exists a necessary causal connection, a causal nexus of appearances, and that in accordance therewith the entire world knowable to us constitutes a uniform whole, a 'monon.' It maintains further that all phenomena are produced by mechanical causes, not by preconceived purposive causes. There is no such thing as a ‘free will’ in the ordinary sense. On the contrary, those very phenomena which we have accustomed ourselves to view as the freest and most independent, the manifestations of the human will, appear in the light of the monistic world-conception as subordinated to just as rigid laws as any other phenomenon of nature” (Haeckel, Anthropogenesis, p. 851 et seq.). It is the monistic philosophy which first shows the phenomenon of free will in the right light. As a bit cut out of the general happening of the world, the human will stands under the same laws as all other natural things and processes. It is conditioned according to natural law. But inasmuch as the monistic view denies the presence of higher, purposeful causes in the course of Nature, it at the same time also declares the will independent of such a higher world-order.
The natural course of evolution leads the processes of Nature upwards to human self-consciousness. On that level it leaves man to himself; henceforward he can draw the impulses of his action from his own spirit. If a universal world-reason were ruling, then man also could not draw his goals from within himself, but only from this eternal reason. In the monistic sense man's action is hereafter determined by causal moments; in the ethical sense it is not determined, because Nature as a whole is determined not ethically but in accordance with natural law. The preliminary stages of ethical conduct are already to be found among the lower organisms. “Even though later the moral foundations have in man developed themselves much more highly, nevertheless their most ancient, prehistoric source lies, as Darwin has shown, in the social instincts of the animals” (Haeckel, Monism, p. 29).
Man's moral conduct is a product of evolution. The moral instinct of animals perfects itself, like everything else in Nature, by inheritance and adaptation, until man sets before himself moral purposes and goals from out of his own spirit. Moral goals appear not as predetermined by a supernatural world-order, but as a new formation within the natural process. Regarded ethically, “that only has purpose which man has first endowed therewith, for only through the realisation of an idea does anything purposeful arise. But only in man does the idea become effective in a realistic sense. To the question, What is man's task in life? Monism can only answer, that which he sets himself. My mission in the world is no (ethically) predetermined one; on the contrary, it is, at every moment, that which I elect for myself. I do not enter on life's journey with a fixed, settled line of march” (cp. my The Philosophy of Freedom, p. 172 et seq.). Dualism demands submission to ethical commands derived from somewhere or other. Monism throws man wholly upon himself. Man receives ethical standards from no external world-being, but only from the depths of his own being. The capacity for creating for oneself ethical purposes may be called moral phantasy. Thereby man elevates the ethical instincts of his lower ancestors into moral action, as through his artistic phantasy he reflects on a higher level in his works of art the forms and occurrences of Nature.
[ 37 ] The philosophical considerations which result from the fact of self-observation thus constitute no refutation, but rather an important complement of the means of proof in favour of the monistic world-conception, derived from comparative anatomy and physiology.
III
[ 38 ] The famous pathologist, Rudolf Virchow,6See note on Virchow and Darwin, below. has taken up a quite peculiar position towards the monistic world-conception. After Haeckel had delivered his address on The Present Theory of Evolution in Relation to Science as a Whole at the fiftieth congress of German scientists and doctors, in which he ably expounded the significance of the monistic world-conception for our intellectual culture and also for the whole system of public instruction, Virchow came forward four days later as his opponent with the speech: The Freedom of Science in the Modern State. At first it seemed as if Virchow wanted monism excluded from the schools only, because, according to his view, the new doctrine was only an hypothesis and did not represent a fact established by definite proofs. It certainly seems remarkable that a modern scientist wants to exclude the doctrine of evolution from school-teaching on the ostensible ground of lack of unassailable proofs while at the same time speaking in favour of Church dogma. Does not Virchow even say (on p. 29 of the speech mentioned): “Every attempt to transform our problems into set formula, to introduce our suppositions as the basis of instruction, especially the attempt simply to dispossess the Church and replace its dogmas without more ado by a ‘descent-religion;’ yes, gentlemen, this attempt must fail entirely, and in its frustration this attempt will also bring with it the greatest dangers for the whole position of science!” One must needs, however, here raise the question—meaningless for every reasonable thinker—Have we more certain proofs for the Church's dogmas than for the “descent-religion?” But it results from the whole tone and style in which Virchow spoke that he was much less concerned about warding off the dangers which monism might cause to the teaching of the young than about his opposition on principle to Haeckel's world-conception as a whole. This he has proved by his whole subsequent attitude. He has seized upon every opportunity that seemed to him suitable to combat the natural history of evolution and to repeat his favourite phrase, “It is quite certain that man does not descend from the ape.” At the twenty-fifth anniversary of the German Anthropological Society, on 24th August, 1894, he even went so far as to clothe this dictum in the somewhat tactless words: “On the road of speculation people have come to the ape theory; one might just as well have arrived at an elephant theory or a sheep theory.” Of course, this utterance has not the smallest sense in view of the results of comparative zoology. “No zoologist,” remarks Haeckel, “would consider it possible that man could have descended from the elephant or the sheep. For precisely these two mammals happen to belong to the most specialised branches of hoofed animals, an order of mammalia which stands in no sort of direct connection with that of the apes or primates (excepting their common descent from an ancestral form common to the entire class).” Hard as it may be towards a meritorious scientist, one can only characterise such utterances as Virchow's as empty verbalism.7On 3rd October, 1898, Virchow delivered the second of the Huxley Lectures in the Charing Cross Hospital Medical School, in London, wherein he said: “I venture to assume that such a duty would not have been assigned to me if those who did so had not known how deep the feeling of veneration for Huxley is in my soul, if they had not seen how I have recognised his achievements from the first pioneer publications of the deceased master, and how greatly I have valued the friendship which he bestowed upon me personally.” Now, these pioneer publications of Huxley's mean precisely the first great step towards the building up of the theory of man's descent from the ape, which Virchow combats, and about which, moreover, in his Huxley address, The more recent Advances of Science, he has nothing more to say than a few words, which are wholly meaningless in face of the present position of this question: “One may think as one chooses about the origin of man, the conviction as to the fundamental coincidence of the human and the animal organisation is at present generally accepted ...” etc.
In combating the theory of descent, Virchow follows quite peculiar tactics. He demands unassailable proofs for this theory. But as soon as natural science discovers anything which is capable of enriching the chain of proofs with a fresh link, he seeks to weaken its probatory force in every way. The theory of descent sees in the famous skulls of Neanderthal, Spy, etc., isolated palaeontological remains of extinct races of lower men, which form a transition-link between the ape-like ancestor of man (Pithecanthropus) and the lower human races of the present day. Virchow declares these skulls to be abnormal, diseased formations, pathological productions. He even developed this contention in the direction of maintaining that all deviations from the fixed organic root-forms must be regarded as pathological formations. If, then, by artificial breeding we produce table-fruit from wild fruit, we have only produced a diseased object in Nature. One cannot prove more effectively the thesis of Virchow (hostile to any theory of evolution), “The plan of organisation is unalterable within the species, kind does not depart from kind,” than by declaring that what shows plainly how kind departs from kind, is not a healthy, natural product of evolution, but a diseased formation. Quite in accord with this attitude of Virchow's to the theory of descent were, further, his assertions in regard to the skeleton remains of the man-ape (Pithecanthropus erectus), which Eugen Dubois found in Java in 1894.
It is true that these remains—the top of the skull, a thigh-bone, and some teeth—were incomplete; and a debate that was most interesting arose about them in the Zoological Congress at Leyden. Out of twelve zoologists, three were of opinion that the remains were those of an ape, three that they were those of a human being, while six defended the view that they belonged to an extinct transition form, between man and ape. Dubois set out in a most lucid manner the relation of this intermediate link between man and ape, on the one hand to the lower races of humanity, on the other to the known anthropoid apes. Virchow declared that the skull and the thigh-bone did not belong together; but that the former came from an ape, the latter from a human being. This assertion was refuted by well-informed palaeontologists, who, on the basis of the conscientious report of the find, expressed themselves as of opinion that not the smallest doubt could exist as to the origin of the bony remains from one and the same individual. Virchow tried to prove that the thigh-bone could only have come from a man, from the presence of a bony outgrowth which could only proceed from an illness that had been cured through careful human nursing. As against that, the palaeontologist Marsh showed that similar bony outgrowths occur also in wild apes. A third assertion of Virchow's, that the deep groove between the upper edge of the eye sockets and the low roof of the skull in Pithecanthropus bore witness to its simian nature, was refuted by the palaeontologist Nehring's showing that the same formation existed in a human skull from Santos in Brazil.
[ 39 ] Virchow's fight against the evolution doctrine appears indeed somewhat of a riddle when one reflects that this investigator, at the beginning of his career, before the publication of Darwin's Origin of Species, defended the doctrine of the mechanical basis of all vital activity. In Würzburg, where Virchow taught from 1848 to 1856, Haeckel sat “reverentially at his feet and first heard with enthusiasm from him that clear and simple doctrine.” But Virchow fights against the doctrine of transformation created by Darwin, which furnishes an all-embracing principle of explanation of that doctrine. When, in the face of the facts of palaeontology, of comparative anatomy and physiology, he constantly emphasises that “definite proof” is lacking, one can only point out, on the other side, that knowledge of the facts alone does indeed not suffice for the recognition of the doctrine of evolution, but there is needed in addition—as Haeckel remarks—a “philosophical understanding” as well. “The unshakable structure of true monistic science arises only through the most intimate interaction and mutual penetration of philosophy and experience” (Haeckel, Natürliche Schöpfungsgeschichte, 34, Vortrag). In any case, the campaign which Virchow has carried on for many years past against the doctrine of descent, with the applause of theological and other reactionaries, is more dangerous than all the mischief which a “descent-religion” can cause in unripe heads. A technical discussion on the point with Virchow is made difficult by the fact that, fundamentally, he remains standing on a bare negation, and in general does not bring forward any specific technical objections against the doctrine of evolution.
[ 40 ] Other scientific opponents of Haeckel's make it easier for us to attain clearness in regard to them because they give the reasons for their opposition, and we can thus recognise the mistakes in their inferences. Among these are to be reckoned Wilhelm His and Alexander Goette.
[ 41 ] His made his appearance in the year 1868 with his Researches as to the First Beginnings of the Vertebrate Body. His attack was primarily directed against the doctrine that the form-development of a higher organism from the first germ to the fully-developed condition can be explained from the evolution of the type. We ought not, according to him, to explain this development by regarding it as the outcome of the generations from which the single organism descends through inheritance and adaptation, but we should seek in the individual organism itself the mechanical causes of its becoming, without regard to comparative anatomy and ancestral history. His starts from the view that the germ, conceived as a uniform surface, grows unequally at different spots, and he asserts that in consequence of this unequal growth the complex structure of the organism results in the course of development. He says: “Take a simple layer and imagine that it possesses at different places a different impulse to enlargement. One will then be able to develop from purely mathematical and mechanical laws the condition in which the formation must find itself after a certain time. Its successive forms will accurately correspond to the stages of development which the individual organism runs through from the germ to the perfected condition. Thus we do not need to go beyond the consideration of the individual organism in order to understand its development, but can deduce this from the mechanical law of growth.
“All formation, whether consisting in cleavage, in the formation of folds, or in complete separation, follows as a consequence from this fundamental law.” The law of growth brings into existence the two pairs of limbs as follows: “Their disposition is determined, like the four corners of a letter, by the crossing of four folds which limit and bound the body.” His rejects any help drawn from the history of the species, with the following justification: “When the history of development for any given form has thoroughly fulfilled the task of its physiological deduction, then it may rightly say of itself that it has explained this form as an individual form” (cp. His, Unsere Körperform und das physiologische Problem ihrer Entstehung). In reality, however, nothing whatever has been accomplished by such an explanation. For the question still remains: Why do different forces of growth work at different spots in the germ? They are simply assumed by His to exist. The explanation can only be seen in the fact that the relations of growth of the individual parts of the germ have been transmitted by inheritance from the ancestral animals, that therefore the individual organism runs through the successive stages of its development because the changes which its forefathers have undergone through long ages continue to operate as the cause of its individual becoming.
[ 42 ] To what consequences the view of His leads may best be seen from his theory as to the orbital lobule, by which the so-called “rudimentary organs” of the organism were to be explained. These are parts which are present in the organism without possessing any sort of significance for its life. Thus man has a fold of skin at the inner corner of his eye which is without any purpose for the functions of the organ of sight. He possesses also muscles corresponding to those by which certain animals can move their ears at will. Yet most people cannot move their ears. Some animals possess eyes which are covered over with a skin and thus cannot serve for seeing. His explains these organs as being such, to which “up to the present it has not been possible to assign any physiological role, analogous to the snippets, which, in cutting out a dress, cannot be avoided even with the most economical use of the stuff.” The evolution theory gives the only possible explanation of them. They are inherited from remote ancestors, in whom they subserved a useful purpose. Animals which to-day live underground and have no seeing eyes, descend from such ancestors as once lived in the light and needed eyes. In the course of many generations the conditions of life of such an organic stock have changed. The organisms have adapted themselves to the new conditions in which they can dispense with organs of sight. But these organs remain as heirlooms from an earlier stage of evolution; only in the course of time they have become atrophied, because they have not been used. These rudimentary organs8Purposeless organs. As to these organs Haeckel observes in his book Die Welträtsel, p. 306: “All higher animals and plants, indeed all those organisms whose bodies are not quite simply built, but are composed of several organs working purposefully together, reveal on attentive examination a number of useless or ineffective, yes, even of dangerous and harmful, arrangements. ... The explanation of these purposeless arrangements is quite simply given by the theory of descent. It shows that these rudimentary organs are atrophied, and that by want of use. ... The blind struggle for existence between the organs conditions just as much their historical destruction, as it originally caused their arising and development.” form one of the strongest means of proof for the natural theory of evolution. If any deliberate intentions whatever had ruled in the building up of an organic form, whence came these purposeless parts? There is no other possible explanation of them, except that in the course of many generations they have gradually fallen into disuse.
[ 43 ] Alexander Goette, also, is of opinion that it is unnecessary to explain the developmental stages of the individual organism by the roundabout road through the history of the species. He deduces the shaping of the organism from a “law of form” which must superadd itself to the physical and chemical processes of matter in order to form the living creature. He endeavoured to defend this standpoint exhaustively in his Entwickelungs-geschichte der Unke (1875). “The essence of development consists in the complete but gradual introduction into the existence of certain natural bodies of a new moment, determined from without, viz., that of the law of form.” Since the law of form is supposed to superadd itself from without to the mechanical and physical properties of matter, and not to develop itself from these properties, it can be nothing else but an immaterial idea, and we have nothing given us therein which is substantially different from the creative thoughts, which, according to the dualistic world-conception, underlie organic forms. It is supposed to be a motive-power existing outside of organised matter and causing its development. That means, it employs the laws of matter as “helpers,” just like Eduard von Hartmann's idea. Goette is forced to call in the help of this “law of form,” because he believes that “the individual developmental history of organisms” alone explains and lies at the basis of their whole shaping. Whoever denies that the true causes of the development of the individual being are an historical result of its ancestral development, will be driven of necessity to have recourse to such ideal causes lying outside of matter.
[ 44 ] Weighty evidence against such attempts to introduce ideal formative forces into the developmental history of the individual, is afforded by the achievements of those investigators who have really explained the forms of higher living creatures on the assumption that these forms are the hereditary repetition of innumerable historical changes in the history of the species, which have occurred during long ages. A striking example in this respect is the “vertebral theory of the skull-bones,” already dimly anticipated by Goethe and Oken, but first set in the right light by Carl Gegenbauer on the basis of the theory of descent. He demonstrated that the skull of the higher vertebrates, and also that of man, has arisen from the gradual transformation of a “root-skull” whose form is still preserved by the “root-fishes,” or primordial gastrea, in the formation of the head. Supported by such results, Gegenbauer therefore remarks rightly: “The descent theory will likewise find a touch-stone in comparative anatomy. Hitherto there existed no observation in comparative anatomy which contradicts it; all observations rather lead us towards it. Thus that theory will receive back from comparative anatomy what it gave to its method: clearness and certainty” (cp. the Introduction to Gegenbauer's Vergleichende Anatomie). The descent theory has directed science to seek for the real causes of the individual development of each organism in its ancestry; and natural science on this road replaces the ideal laws of development which might be supposed to superpose themselves on organic matter, by the actual facts of the ancestral history, which continue to operate in the individual creature as formative forces.
[ 45 ] Under the influence of the theory of descent, science is ever drawing nearer to that great goal which one of the greatest scientists of the century, Karl Ernst von Baer, has depicted in the words: “It is one fundamental thought which runs through all forms and stages of animal evolution and dominates all particular conditions. It is the same fundamental thought which gathered together the scattered masses of the spheres in universal space and formed them into solar systems; the same thought caused the disintegrated dust on the surface of the planet to sprout forth into living forms. But this thought is nothing else but Life itself, and the words and syllables wherein it expresses itself are the various forms of that which lives.” Another utterance of Baer's gives the same conception in another form: “To many another will a prize fall. But the palm will be won by the fortunate man for whom it is reserved to trace back the formative energies of the animal body to the general forces and vital functions of the universe as a whole.”
[ 46 ] It is these same general forces of Nature which cause the stone lying on an inclined plane to roll downwards, which also, through evolution, cause one organic form to arise from another. The characteristics which a given form acquires through many generations by adaptation, it hands on by heredity to its descendants. That which an organism unfolds to-day, from within outwards, from its germinal dispositions, had developed itself outwardly in its ancestors in mechanical struggle with the rest of the forces of Nature. In order to hold this view firmly it is doubtless necessary to assume that the formations acquired in this external struggle should be actually transmitted by heredity. Hence the whole doctrine of evolution is called in question by the view, defended especially by August Weismann, that acquired characteristics are not inherited. He is of opinion that no external change which has occurred in an organism can be transmitted to its offspring, but that only can be inherited which is predetermined by some original disposition in the germ. In the germ-cells of organisms innumerable possibilities of development are held to lie. Accordingly, organic forms can vary in the course of reproduction. A new form arises when among the descendants possibilities of development come to unfoldment other than in the ancestors.
From among the ever new forms arising in this way, those will survive which can best maintain the struggle for existence. Forms unequal to the struggle will perish. When out of a possibility of evolution a form develops itself which is specially effective in the battle of competition, then this form will reproduce itself; when that is not the case, it must perish. One sees that here causes operating on the organism from without are entirely eliminated. The reasons why the forms change lie in the germ. And the struggle for existence selects from among the forms coming into existence from the most diverse germ-dispositions those which are the fittest. The special characteristic of an organism does not lead us up to a change which has occurred in its ancestors as its cause, but to a disposition in the germ of that ancestor. Since, therefore, nothing can be effected from outside in the upbuilding of organic forms, it follows that already in the germ of the root-form, from which a race began its development, there must have lain the dispositions for the succeeding generations.
We find ourselves once more in face of a doctrine of Chinese boxes one within another. Weismann conceives of the progressive process through which the germs bring about evolution, as a material process. When an organism develops, one portion of the germ-mass out of which it evolves is solely employed in forming a fresh germ for the sake of further reproduction. In the germ-mass of a descendant, therefore, a part of that of the parents is present, in the germ-mass of the parents a portion of that of the grandparents, and so on backwards to the root-form. Hence through all organisms developing one from another there is maintained an originally present germ-substance. This is Weismann's theory of the continuity and immortality of the germ-plasm. He believes himself to be forced to this view, because numerous facts appear to him to contradict the assumption of the inheritance of acquired characteristics. As one specially noteworthy fact he cites the presence of the workers, who are incapable of reproduction, among the communal insects—bees, ants, and termites. These workers are not developed from special eggs, but from the same as those from which spring the fruitful individuals. If the female larvae of these animals are very richly and nourishingly fed, they then lay eggs from which queens or males proceed. If the feeding is less generous, the result is the production of sterile workers. Now, it is very easy and obvious to seek the cause of this unfruitfulness simply in the less effective nourishment.
This view is represented among others by Herbert Spencer, the English thinker, who has constructed a philosophical world-conception on the basis of natural evolution. Weismann holds this view to be mistaken. For in the worker-bee the reproductive organs do not merely remain behindhand in their development, but they actually become rudimentary; they do not possess a large proportion of the parts necessary for reproduction. But now, he contends, one can demonstrate in the case of other insects that defective nourishment in no way entails such a degeneration of organs. Flies are insects related to bees. Weismann reared the eggs laid by a female bluebottle in two separate batches, and fed the one plentifully, the other meagrely. The latter grew slowly and remained strikingly small. But they reproduced themselves. Hence it appears that in flies insufficient nourishment does not produce sterility. But then it follows also that in the root-insect, the common ancestral form, which in line with the evolution doctrine must be assumed for the allied species of bees and flies, this peculiarity of being rendered unfruitful by insufficient nourishment cannot have existed. On the contrary, this unfruitfulness must be an acquired characteristic of the bees. But at the same time there can be no question of any inheritance of this peculiarity, for the workers which have acquired it do not reproduce themselves, and accordingly, therefore, can pass on nothing by heredity. Hence the cause must be sought for in the bee-germ itself, why at one time queens and at another workers are developed. The external influence of insufficient nourishment can accomplish nothing, because it is not inherited. It can only act as a stimulus, which brings to development the preformed disposition in the germ.
Through the generalisation of these and similar results, Weismann comes to the conclusion: “The external influence is never the real cause of the difference, but plays the part of the stimulus, which decides which of the available dispositions shall come to development. The real cause, however, always lies in preformed changes of the body itself, and these—since they are constantly purposeful—can be referred in their development only to processes of selection,” to the selection of the fittest in the struggle for existence. The struggle for existence (selection) “alone is the guiding and leading principle in the development of the world of organisms” (Aüssere Einflüsse der Entwickelungsreize, p. 49). The English investigators Francis Galton and Alfred Russel Wallace hold the same view as Weismann as to the non-inheritance of acquired characteristics and the omnipotence of selection.
[ 47 ] The facts which these investigators advance are certainly in need of explanation. But they cannot receive such an explanation in the direction indicated by Weismann without abandoning the entire monistic doctrine of evolution. But the objections urged against the inheritance of acquired characteristics are the least capable of driving us to such a step. For one only needs to consider the development of the instincts in the higher animals to convince oneself of the fact that such inheritance does occur. Look, for instance, at the development of our domestic animals. Some of them, as a consequence of living together with men, have developed mental capacities which cannot even be mentioned in connection with their wild ancestors. Yet these capacities can certainly not proceed from an inner disposition. For human influence, human training, comes to these animals as something wholly external. How could an inner disposition possibly come to meet exactly an arbitrarily determined action of man? And yet training becomes instinct, and this is inherited by the descendants. Such an example cannot be refuted. And countless others of the same kind can be found. Thus the fact of the inheritance of acquired characteristics remains such; and we must hope that further investigations will bring the apparently contradictory observations of Weismann and his followers into harmony with monism.
[ 48 ] Fundamentally, Weismann has only stopped half-way to dualism. His inner causes of evolution only have a meaning when they are ideally conceived. For, if they were material processes in the germ-plasm, it would be unintelligible why these material processes and not those of external happenings should continue to operate in the process of heredity. Another investigator of the present day is more logical than Weismann—namely, J. Reinke, who, in his recently published book, Die Welt als That; Umrisse einer Weltansicht auf naturwissenschaftlicher Grundlage, has taken unreservedly the leap into the dualistic camp. He declares that a living creature can never build itself up from out of the physical and chemical forces of organic substances. “Life does not consist in the chemical properties of a combination, or a number of combinations. Just as from the properties of brass and glass there does not yet emerge the possibility of the production of the microscope, so little does the origination of the cell follow from the properties of albumen, carbohydrates, fats, lecithin, Cholesterin, etc.” (p. 178 of the above-named work). There must be present besides the material forces also spiritual forces, or at least forces of another order, which give the former their direction, and so regulate their combined action that the organism results therefrom. These forces of another order Reinke calls “dominants.” “In the union of the dominants with the energies—the operations of the physical and chemical forces—there unveils itself to us a spiritualisation of Nature; in this mode of conceiving things culminates my scientific confession of faith” (p. 455). It is now only logical that Reinke also assumes a universal world-reason, which originally brought the purely physical and chemical forces into the relation in which they are operative in organic beings.
[ 49 ] Reinke endeavours to escape from the charge that through such a reason working from outside upon the material forces, the laws which hold good in the inorganic kingdom are rendered powerless for the organic world, by saying: “The universal reason, as also the dominants, make use of the mechanical forces; they actualise their creations only by the help of these forces. The attitude of the world-reason coincides with that of a mechanician, who also lets the natural forces do their work after he has imparted to them their direction.” But with this statement the kind of conformity to law which expresses itself in mechanical facts is once more declared to be the helper of a higher kind of law, in the sense of Eduard von Hartmann.
[ 50 ] Goette's law of form, Weismann's inner causes of development, Reinke's dominants are fundamentally just nothing else but derivatives of the thoughts of the world-creator who builds according to plan. As soon as one forsakes the clear and simple mode of explanation of the monistic world-conception, one inevitably falls a victim to mystical-religious conceptions, and of such Haeckel's saying holds good, that “then it is better to assume the mysterious creation of the individual species” (Uber unsere gegenwärtige Kenntniss vom Ursprung des Menschen, p. 30).
[ 51 ] Besides those opponents of monism who are of opinion that the contemplation of the phenomena of the world leads up to spiritual beings, who are independent of material phenomena, there are still others9Other opponents of Haeckel. Here we can only speak of such objections to Haeckel's doctrines as are, to a certain extent, typical and have their origin in antiquated, although still always influential, circles of thought. The numerous “refutations” of Haeckel, which present themselves merely as variants of the main objections cited, have to be left unnoticed equally with those which Haeckel himself has disposed of in his book on Die Welträtsel, by saying to these valiant warriors, “Acquire by a diligent five years' study of natural science, and in particular of anthropology (especially the anatomy and the physiology of the brain!), that indispensable empirical prior knowledge of the facts, which you still lack entirely.” who seek to save the domain of a supernatural order hovering over the natural one, by denying entirely to man's power of knowing the capacity to understand the ultimate grounds of the world-happenings.10Limits of knowledge. In my Philosophie der Freiheit I have shown the misunderstanding upon which is based the assumption of limits of knowledge. The ideas of these opponents have found their most eloquent spokesman in Du Bois-Reymond. His famous “Ignorabimus” speech, delivered at the Forty-fifth Congress of German Scientists and Doctors (1872), is the expression of their confession of faith. In this address Du Bois-Reymond describes as the highest goal of the scientist the explanation of all world-happenings, therefore also of human thinking and feeling, by mechanical processes. If some day we shall succeed in saying how the parts of our brain lie and move when we have a definite thought or feeling, then the goal of natural explanation will have been reached. We can get no further. But, in Du Bois-Reymond's view, we have not therewith understood in what the nature of our spirit consists. “It seems, indeed, on superficial examination, as though, through the knowledge of the material processes in the brain, certain mental processes and dispositions might become intelligible. Among such I reckon memory, the flow and association of ideas, the consequences of practice, the specific talents, and so on. A minimum of reflection, however, shows that this is a delusion. Only with regard to certain inner conditions of the mental life, which are somehow of like significance with the outer ones through sense impressions, shall we thus be instructed, not with regard to the coming about of the mental life through these conditions.
“What thinkable connection exists between the definite movements of definite atoms in my brain on the one hand; and, on the other, those for me primary, not further definable, not to be denied facts: ‘I feel pain, I feel pleasure, I taste something sweet, smell the odour of roses, hear the sound of an organ, see red,’ and the equally immediate certainty flowing therefrom, ‘therefore I am!’? It is just entirely and for ever incomprehensible that it should not be indifferent to a number of carbon, oxygen, nitrogen, hydrogen, etc., atoms, how they lie and move, how they lay and moved, how they will lie and move.”
But who asked Du Bois-Reymond first to expel mind from matter, in order then to be able to observe that mind is not in matter? The simple attraction and repulsion of the tiniest particle of matter is force, therefore a spiritual cause proceeding from the substance. From the simplest forces we see the complicated human mind building itself up in a series of developments; and we understand it from this its becoming. “The problem of the origin and nature of consciousness is only a special case of the general problem in chief: that of the connection of matter and force” (Haeckel, Freie Wissenschaft and freie Lehre, p. 80). As a matter of fact, the problem is not at all, How does mind arise out of mindless matter? but, How does the more complex mind develop itself out of the simplest mental (or spiritual) actions of matter—out of attraction and repulsion? In the preface which Du Bois-Reymond has written to the reprint of his “Ignorabimus” speech, he recommends to those who are not contented with his declaration of the unknowableness of the ultimate grounds of being, that they should try to get along with the faith-conceptions of the supernatural view of the world. “Let them, then, make a trial of the only other way of escape, that of supernaturalism. Only that where supernaturalism begins, science ceases.” But such a confession as that of Du Bois-Reymond will always open the doors wide to supernaturalism. For whenever one sets a limit to the knowledge of the human mind, there it will surely start the beginning of its belief in the “no longer knowable.”
[ 52 ] There is only one salvation from the belief in a supernatural world-order, and that is the monistic insight that all grounds of explanation for the phenomena of the world lie also within the domain of these phenomena. This insight can only be given by a philosophy which stands in the most intimate harmony with the modern doctrine of evolution.
Haeckel Und Seine Gegner
Vorrede
[ 1 ] Von meiner vor fünf Jahren veröffentlichten «Philosophie der Freiheit» habe ich die Überzeugung, daß sie das Bild einer Weltanschauung gibt, die mit den gewaltigen Ergebnissen der Naturwissenschaften unserer Zeit in vollem Einklang steht. Ich bin mir bewußt, daß ich diesen Einklang nicht absichtlich herbeigeführt habe. Mein Weg war ganz unabhängig von dem, welchen die Naturwissenschaft einschlägt.
[ 2 ] Aus dieser Unabhängigkeit meiner Vorstellungsart von dem herrschenden Wissensgebiet unserer Tage und aus der gleichzeitigen völligen Übereinstimmung mit demselben glaube ich die Berechtigung herleiten zu dürfen, die Stellung des monumentalsten Vertreters der naturwissenschaftlichen Denkweise, Ernst Haeckels, innerhalb des Geisteskampfes unserer Zeit darzustellen.
[ 3 ] Das Bedürfnis, sich mit der Naturwissenschaft auseinanderzusetzen, wird zweifellos heute von vielen empfunden. Es kann am besten dadurch befriedigt werden, daß man sich in die Ideen desjenigen Naturforschers vertieft, der am rückhaltlosesten die Konsequenzen der naturwissenschaftlichen Voraussetzungen gezogen hat. Ich möchte mich mit diesem Schriftchen an diejenigen wenden, die mit mir in dieser Beziehung ein gleiches Bedürfnis empfinden.
Berlin, im Januar 1900.
[ 4 ] Der Empfindung, welche der Mensch hat, wenn er seine Stellung innerhalb der Welt betrachtet, hat Goethe einen herrlichen Ausdruck in seinem Buche über Winckelmann gegeben: «Wenn die gesunde Natur des Menschen als ein Ganzes wirkt, wenn er sich in der Welt als in einem großen, schönen, würdigen und werten Ganzen fühlt, wenn das harmonische Behagen ihm ein reines, freies Entzücken gewährt: dann würde das Weltall, wenn es sich selbst empfinden könnte, als an sein Ziel gelangt, aufjauchzen und den Gipfel des eigenen Werdens und Wesens bewundern.» Aus dieser Empfindung heraus entspringt die bedeutungsvollste Frage, die sich der Mensch stellen kann: Wie ist sein eigenes Werden und Wesen mit demjenigen des ganzen Weltalls verknüpft? Schiller hat den Weg, durch den Goethe zur Erkenntnis der menschlichen Natur kommen wollte, trefflich in einem Briefe an diesen am 23. August 1794 bezeichnet. «Von der einfachen Organisation steigen Sie, Schritt vor Schritt, zu den mehr verwickelten hinauf, um endlich die verwickeltste von allen, den Menschen, genetisch aus den Materialien des ganzen Naturgebäudes zu erbauen.» Dieser Weg Goethes ist nun auch der, welchen die Naturwissenschaft seit vier Jahrzehnten einschlägt, um die «Frage aller Fragen für die Menschheit» zu lösen. Huxley sieht sie darin, die Stellung zu bestimmen, welche «der Mensch in der Natur einnimmt, und seine Beziehungen zu der Gesamtheit der Dinge». Es ist das große Verdienst Charles Darwins, dem Nachdenken über diese Frage einen neuen naturwissenschaftlichen Boden geschaffen zu haben. Die Tatsachen, die er 1859 in seinem Werke «Über die Entstehung der Arten» mitteilte, und die Grundsätze, die er entwickelte, boten der Naturforschung die Möglichkeit, auf ihre Weise zu zeigen, wie begründet Goethes Überzeugung war, daß die Natur «nach tausendfältigen Tieren ein Wesen bildet, das sie alle enthält: den Menschen». Heute blicken wir auf vierzig Jahre wissenschaftlicher Entwickelung zurück, die unter dem Einflusse der Ideenrichtung Darwins stehen. Mit Recht konnte Ernst Haeckel in seiner Schrift «Über unsere gegenwärtige Kenntnis vom Utsprung des Menschen», die einen von ihm auf dem vierten internationalen Zoologen-Kongreß in Cambridge am 26. August 1898 gehaltenen Vortrag wiedergibt, sagen: «Vierzig Jahre Darwinismus! Welcher ungeheure Fortschritt unserer Naturerkenntnis! Und welcher Umschwung unserer wichtigsten Anschauungen, nicht allein in den nächstbetroffenen Gebieten der gesamten Biologie, sondern auch in demjenigen der Anthropologie und ebenso aller sogenannten Geisteswissenschaften! » Goethe hat aus seiner tiefen Naturerkenntnis heraus diesen Umschwung vorausgesehen und seine Bedeutung für den Fortgang der menschlichen Geisteskultur in vollem Umfange erkannt. Wir sehen das besonders deutlich aus einem Gespräche, das er am 2. August 1830 mit Soret gehabt hat. Damals gelangten die Nachrichten von der begonnenen Julirevolution nach Weimar und versetzten alles in Aufregung. Soret wurde, als er Goethe besuchte, mit den Worten empfangen: «Nun, was denken Sie von dieser großen Begebenheit? Der Vulkan ist zum Ausbruch gekommen; alles steht in Flammen, und es ist nicht ferner eine Verhandlung bei geschlossenen Türen!» Soret konnte natürlich nur glauben, Goethe spreche von der Julirevolution, und erwiderte, daß bei den bekannten Zuständen nichts anderes zu erwarten war, als daß man mit der Vertreibung der königlichen Familie endigen würde. Goethe aber hatte etwas ganz anderes im Sinne. «Ich rede gar nicht von jenen Leuten; es handelt sich bei mir um ganz andere Dinge. Ich rede von dem in der Akademie zum öffentlichen Ausbruch gekommenen, für die Wissenschaft so höchst bedeutenden Streit zwischen Cuvier und Geoffroy de Saint-Hilaire!» Der Streit betraf die Frage, ob jede der Spezies, in denen die organische Natur sich auslebt, einen besonderen Bauplan für sich habe oder ob ihnen allen ein solcher gemeinsam sei. Goethe hatte für sich diese Frage bereits mehr als vierzig Jahre früher entschieden. Sein eifriges Studium der Pflanzen- und Tierwelt hatte ihn zum Gegner der Linnéschen Ansicht gemacht, daß wir «Spezies so viele zählen, als verschiedene Formen im Prinzip geschaffen worden sind». Wer eine solche Meinung hat, kann sich nur bemühen zu erforschen, welches die Organisationspläne der einzelnen Spezies sind. Er wird diese einzelnen Formen vor allem sorgfältig zu unterscheiden suchen. Goethe schlug einen anderen Weg ein. «Das, was Linné mit Gewalt auseinanderzuhalten suchte, mußte, nach dem innersten Bedürfnis meines Wesens, zur Vereinigung anstreben.» Es bildete sich in ihm die Meinung aus, die er 1796 in den «Vorträgen über die drei ersten Kapitel des Entwurfs einer allgemeinen Einleitung in die vergleichende Anatomie» in dem Satze zusammengefaßt hat: «Dies also hätten wir gewonnen, ungescheuet behaupten zu dürfen, daß alle vollkommnern organischen Naturen, worunter wir Fische, Amphibien, Vögel, Säugetiere und an der Spitze der letzten den Menschen sehen, alle nach einem Urbilde geformt seien, das nur in seinen sehr beständigen Teilen mehr oder weniger hin und her weicht und sich noch täglich durch Fortpflanzung aus- und umbildet.» Das Urbild, auf das sich alle mannigfaltigen Pflanzenformen zurückführen lassen, hat Goethe schon 1790 in seinem «Versuch, die Metamorphose der Pflanzen zu erklären» dargestellt. Diese Betrachtungsweise, durch die Goethe die Gesetze der lebendigen Natur zu erkennen bestrebt war, ist ganz gleich derjenigen, die er in seinem 1793 geschriebenen Aufsatz «Der Versuch als Vermittler von Objekt und Subjekt» für die leblose Welt fordert: «In der lebendigen Natur geschieht nichts, was nicht in einer Verbindung mit dem Ganzen stehe, und wenn uns die Erfahrungen nur isoliert erscheinen, wenn wir die Versuche nur als isolierte Fakta anzusehen haben, so wird dadurch nicht gesagt, daß sie isoliert seien; es ist nur die Frage: Wie finden wir die Verbindung dieser Phänomene, dieser Begebenheiten?» Auch die Spezies erscheinen uns nur isoliert. Goethe sucht ihre Verbindung. Daraus geht klar hervor, daß Goethes Streben darauf gerichtet ist, bei Betrachtung der Lebewesen dieselbe Erklärungsart anzuwenden, die bei der leblosen Natur zum Ziele führt.1Goethe und Kant. Den Gegensatz, der zwischen Goethes und Kants Weltanschauung besteht, habe ich in den Einleitungen zu meiner Ausgabe von Goethes naturwissenschaftlichen Schriften (in Kürschner «Deutsche National-Literatur») und in meinem Buche «Goethes Weltanschauung» («Die Metamorphose der Welterscheinungen>) charakterisiert. Er zeigt sich auch in der Stellung der beiden Persönlichkeiten zur Erklärung der organischen Natur. Goethe sucht diese Erklärung auf dem Wege, den auch die moderne Naturwissenschaft betreten hat. Kant hält eine solche Erklärung für unmöglich. Nur wer sich in das Wesen von Goethes Weltansicht vertieft, kann ein richtiges Urteil über ihre Stellung zur Kantschen Philosophie gewinnen. Die Selbstzeugnisse Goethes sind nicht maßgebend, da dieser sich nie in ein genaueres Studium Kants eingelassen hat. «Der Eingang (der «Kritik der reinen Vernunft) war es, der mir gefiel, ins Labyrinth selbst konnt ich mich nicht wagen: bald hinderte mich die Dichtungsgabe, bald der Menschenverstand, und ich fühlte mich nirgend gebessert.» Ihm gefielen einzelne Stellen in Kants «Kritik der Urteilskraft», weil er ihren Sinn so umdeutete, daß er seiner eigenen Weltanschauung entsprach. Es ist daher nur zu begreiflich, daß seine Gespräche mit Kantianern sich wunderlich ausnahmen. «Sie hörten mich wohl, konnten mir aber nichts erwidern, noch irgend förderlich sein. Mehr als einmal begegnete es mir, daß einer oder der andere mit lächelnder Verwunderung zugestand: es sei freilich ein Analogon Kantischer Vorstellungsart, aber ein seltsames.» Karl Vorländer hat in seinem Aufsatz «Goethes Verhältnis zu Kant in seiner historischen Entwicklung» (Kantstudien I, II) dieses Verhältnis nach dem Wortlaut von Goethes Selbstzeugnissen beurteilt und mir vorgeworfen, daß meine Auffassung «mit klaren Selbstzeugnissen Goethes in Widerspruch» stehe und mindestens «stark einseitig» sei. Ich hätte diesen Einwand unerwidert gelassen, weil ich aus den Ausführungen des Herrn Karl Vorländer sah, daß sie von einem Manne herrühren, dem es ganz unmöglich ist, eine ihm fremde Denkweise zu verstehen; allein, es schien mir doch nötig, eine daran geknüpfte Bemerkung nicht ohne Antwort zu lassen. Herr Vorländer gehört nämlich zu denjenigen Menschen, die ihre Meinung für absolut richtig, also aus der höchstmöglichen Einsicht herrührend, ansehen und jede andere zu einem Produkte der Unwissenheit stempeln. Weil ich anders über Kant denke als er, gibt er mir den weisen Rat, gewisse Partien in Kants Werken zu studieren. Eine solche Art der Kritik fremder Meinungen kann nicht stark genug zurückgewiesen werden. Wer gibt jemandem das Recht, mich wegen einer von der seinigen abweichenden Anschauung nicht zu kritisieren, sondern zu schulmeistern? Ich habe daher Herrn Karl Vorländer im 4. Bande meiner Ausgabe von Goethes naturwissenschaftlichen Schriften meine Meinung über diese Schulmeisterei gesagt. Darauf hat er im III. Band der «Kantstudien» mein Buch «Goethes Weltanschauung» in einer Weise besprochen, die nicht nur das vorher wider mich Geleistete der Form nach überbietet, sondern die auch voller odjektiver Unwahrkheiten ist. So spricht er von einer «isolierten und verbitterten Opposition», in der ich mich gegen die gesamte moderne Philosophie (exklusive natürlich Nietzsche) und Naturwissenschaft befinde. Das sind gleich drei objektive Unwahrheiten. Wer meine Schriften liest - und wer über mich urteilt wie Herr Vorländer, sollte sie doch lesen -, wird ersehen, daß ich zwar an einzelnen Anschauungen der modernen Naturwissenschaft sachliche Kritik übe und andere philosophisch zu vertiefen suche, daß aber von einer verbitterten Opposition zu reden geradezu absurd ist. In meiner «Philosophie der Freiheit» habe ich meine Überzeugung dahin ausgesprochen, daß in meinen Anschauungen der philosophische Abschluß des Gebäudes gegeben sei, das «Darwin und Haeckel für die Naturwissenschaft errichtet haben» (XI. «Die moralische Phantasie»). Daß ich es bin, der den Grundmangel in Nietzsches Ideenwelt scharf betont hat, weiß zwar der Franzose Henri Lichtenberger, der in seinem Buche «La philosophie de Nietzsche» sagt: «R. Steiner est l’auteur de Wahrheit und Wissenschaft et Die Philosophie der Freiheit; dans ce dernier ouvrage il complète la théorie de Nietzsche sur un point important.» Er betont, daß ich gezeigt habe, daß gerade Nietzsches «Übermensch» das nicht ist, was er sein sollte. Der deutsche Philosoph Karl Vorländer hat entweder meine Schriften nicht gelesen und urteilt dennoch über mich, oder er hat das getan und schreibt die obigen und ähnliche objektive Unwahrheiten hin. Ich überlasse es dem urteilsfähigen Publikum, zu entscheiden, ob sein Beitrag, der würdig befunden wurde, in eine ernste philosophische Zeitschrift aufgenommen zu werden, ein Beweis für seine gänzliche Urkteilslosigkeit oder ein bedenklicher Beitrag zur deutschen Gelehrten-Moral ist. Wie weit er mit solchen Vorstellungen seiner Zeit vorauseilte, wird ersichtlich, wenn man bedenkt, daß zur selben Zeit, als Goethe seine Metamorphosenschrift veröffentlichte, Kant in seiner «Kritik der Urteilskraft» die Unmöglichkeit einer Erklärung des Lebendigen nach denselben Prinzipien, die für das Leblose gelten, wissenschaftlich dartun wollte. Er behauptet: «Es ist nämlich ganz gewiß, daß wir die organisierten Wesen und deren innere Möglichkeit nach bloß mechanischen Prinzipien der Natur nicht einmal zureichend kennenlernen, viel weniger uns erklären können; und zwar so gewiß, daß man dreist sagen kann, es ist für den Menschen ungereimt, auch nur einen solchen Anschlag zu fassen oder zu hoffen, daß noch etwa deteinst ein Newton aufstehen könne, der auch nur die Erzeugung eines Grashalms nach Naturgesetzen, die keine Absicht geordnet hat, begreiflich machen werde; sondern man muß diese Einsicht den Menschen schlechthin absprechen.» Haeckel weist diesen Gedanken mit den Worten zurück: «Nun ist aber dieser unmögliche Newton siebzig Jahre später in Darwin wirklich erschienen und... und hat die Aufgabe tatsächlich gelöst, die Kant für absolut unlösbar hielt! » Daß der durch den Darwinismus bewirkte Umschwung in den naturwissenschaftlichen Anschauungen eintreten müsse, wußte Goethe, denn er entspricht seiner eigenen Vorstellungsart. In der Ansicht, die Geoffroy de Saint-Hilaire gegen Cuvier verteidigte, daß alle organischen Formen einen «allgemeinen, nur hier und da modifizierten Plan» in sich tragen, erkannte er die eigene wieder. Deshalb konnte er zu Soret sagen: «Jetzt ist nun auch Geoffroy de Saint-Hilaire entschieden auf unserer Seite und mit ihm alle seine bedeutenden Schüler und Anhänger Frankreichs. Dieses Ereignis ist für mich von ganz unglaublichem Wert, und ich juble mit Recht über den endlich erlebten allgemeinen Sieg einer Sache, der ich mein Leben gewidmet habe und die ganz vorzüglich auch die meinige ist.» Von noch viel größerem Werte für Goethes Naturanschauung sind nun die Entdeckungen Darwins. Die Naturanschauung Goethes verhält sich zum Darwinismus in ähnlicher Weise wie die Einsichten Kopernikus’ und Keplers in den Bau und die Bewegungen des Planetensystems zu der Auffindung des Gesetzes der allgemeinen Anziehung aller Himmelskörper durch Newton. Dieses Gesetz zeigt die naturwissenschaftlichen Ursachen auf, warum sich die Planeten in der Weise bewegen, wie es Kopernikus und Kepler beschrieben haben. Und Darwin hat die natürlichen Ursachen gefunden, warum das von Goethe angenommene gemeinsame Urbild aller organischen Wesen in den mannigfaltigen Spezies zur Erscheinung kommt.
[ 5 ] Der Zweifel an der Anschauung, daß jeder einzelnen organischen Spezies ein besonderer Organisationsplan zugrunde liege, der für alle Zeiten unveränderlich sei, setzte sich in Darwin fest auf einer Reise, die er im Sommer 1831 als Naturforscher auf dem Schiffe «Beagle» nach Südamerika und Australien antrat. Wie seine Gedanken reiften, davon erhalten wir eine Vorstellung, wenn wir Mitteilungen von ihm lesen wie diese: «Als ich während der Fahrt des «Beagle den Galapagos-Archipel, der im Stillen Ozean ungefähr fünfhundert englische Meilen von der Küste von Südamerika entfernt liegt, besuchte, sah ich mich von eigentümlichen Arten von Vögeln, Reptilien und Pflanzen umgeben, welche sonst nirgends in der Welt existieren. Doch trugen sie fast alle ein amerikanisches Gepräge an sich. Im Gesang der Spottdrossel, in dem harschen Geschrei des Aasgeiers, in den großen leuchterähnlichen Opuntien nahm ich deutlich die Nachbarschaft mit Amerika wahr; und doch waren diese Inseln durch so viele Meilen Ozean vom Festlande getrennt und wichen in ihrer geologischen Konstitution und in ihrem Klima weit von ihm ab. Noch überraschender war die Tatsache, daß die meisten Bewohner jeder einzelnen Insel dieses kleinen Archipels spezifisch verschieden waren, wenn auch untereinander nahe verwandt... Ich habe mich damals oft gefragt, wie diese vielen eigentümlichen Pflanzen und Tiere entstanden sind. Die einfachste Antwort schien zu sein, daß die Bewohner der verschiedenen Inseln voneinander abstammten und im Verlauf ihrer Abstammung Modifikationen erlitten hätten und daß alle Bewohner des Archipels von denen des nächsten Festlandes, nämlich Amerika, von welchem die Kolonisation natürlich herrühren würde, abstammten. Es blieb mir aber lange ein unerklärliches Problem: wie der notwendige Modifikationsgrad erreicht worden sein könnte.» Über dieses Wie klärten Darwin die zahlreichen Züchtungsversuche auf, die er nach seiner Heimkehr mit Tauben, Hühnern, Hunden, Kaninchen und Kulturgewächsen machte. Aus ihnen ersah er, in welch hohem Grade in den organischen Formen die Möglichkeit liegt, sich im Verlaufe ihrer Fortpflanzung fortwährend zu verändern. Man ist in der Lage, durch Herstellung künstlicher Bedingungen aus einer gewissen Form nach wenigen Generationen neue Arten zu erhalten, die viel mehr voneinander abweichen als solche in der freien Natur, deren Verschiedenheit man für so groß hält, daß man jeder einen besonderen Organisationsplan zugrunde legen möchte. Diese Veränderlichkeit der Arten benutzt bekanntlich der Züchter, um solche Formen von Kulturorganismen zur Entwickelung zu bringen, die gewissen Absichten entsprechen. Er sucht die Bedingungen herzustellen, welche die Veränderung nach einer Richtung hinlenken, die ihm entspricht. Will er eine Schafsorte mit besonders feiner Wolle züchten, so Sucht er innerhalb seiner Schafherde diejenigen Individuen aus, welche die feinste Wolle haben. Diese läßt er sich fortpflanzen. Von ihren Nachkommen wählt er zur weiteren Fortpflanzung wieder diejenigen aus, welche die feinste Wolle haben. Wird das durch eine Reihe von Generationen hindurch fortgesetzt, so erlangt man eine Schafspezies, welche in der Bildung der Wolle erheblich von ihren Vorfahren abweicht. Dasselbe kann man mit andern Eigenschaften der Lebewesen machen. Aus diesen Tatsachen geht zweierlei hervor: daß die organischen Formen die Neigung haben, sich zu verändern, und daß sie die angenommenen Veränderungen auf ihre Nachkommen vererben. Durch die erste Eigenschaft der Lebewesen ist der Züchter imstande, bei seiner Spezies gewisse Merkmale auszubilden, die seinen Zwecken entsprechen; durch die zweite übertragen sich diese neuen Merkmale von einer Generation auf die andere.
[ 6 ] Der Gedanke liegt nun nahe, daß sich die Formen auch in der freien Natur fortwährend ändern. Und die große Veränderungsfähigkeit der Kulturorganismen zwingt nicht dazu, anzunehmen, daß diese Eigenschaft der organischen Formen innerhalb gewisser Grenzen eingeschlossen ist. Wir können vielmehr voraussetzen, daß sich im Laufe großer Zeiträume eine gewisse Form in eine ganz andere verwandelt, die in ihrer Bildung in der denkbar größten Weise von der ersten abweicht. Die natürlichste Folgerung ist dann die, daß die organischen Spezies nicht unabhängig jede nach einem besonderen Bauplan nebeneinander entstanden sind, sondern daß sich im Laufe der Zeit die einen aus den andern entwickeln. Eine Unterstützung erfährt dieser Gedanke durch die Erkenntnisse, zu denen Lyell in der Entwickelungsgeschichte der Erde gelangt ist und die er zuerst 1830 in seinen «Grundsätzen der Geologie» (Principles of geology) veröffentlicht hat. Durch sie wurden jene älteren geologischen Ansichten, wonach sich die Bildung der Erde in einer Reihe gewaltsamer Katastrophen vollzogen haben soll, beseitigt. Durch diese Katastrophenlehre sollten die Ergebnisse erklärt werden, zu denen die Untersuchung der festen Erdkruste geführt hat. Die verschiedenen Schichten der Erdrinde und die in ihnen enthaltenen versteinerten organischen Wesen sind ja die Überbleibsel dessen, was sich im Zeitenlaufe auf der Erdoberfläche zugetragen hat. Die Anhänger der gewaltsamen Umwälzungslehre glaubten, daß sich die Entwickelung der Erde in aufeinanderfolgenden, genau voneinander unterschiedenen Perioden vollzogen habe. Am Ende einer solchen Periode trat eine Katastrophe ein. Alles Lebendige wurde zerstört und seine Reste in einer Erdschicht aufbewahrt. Über dem Zerstörten erhob sich eine vollständig neue Welt, die wieder geschaffen werden mußte. An die Stelle dieser Katastrophenlehre setzte Lyell die Ansicht, daß sich die Erdrinde im Laufe sehr langer Zeiträume allmählich durch dieselben Vorgänge gebildet habe, die sich noch heute jeden Tag auf der Oberfläche der Erde abspielen. Die Tätigkeit der Flüsse, welche Schlamm von einer Stelle ab- und der anderen zuführen, die Wirkungen der Gletscher, die das Gestein abschleifen und Blöcke fortschieben, und ähnliche Vorgänge sind es gewesen, die in ihrer stetigen, langsamen Wirksamkeit der Erdoberfläche die heutige Gestalt gegeben haben. Diese Anschauung zieht die andere notwendig nach sich, daß auch die heutigen Tier- und Pflanzenformen sich allmählich aus denjenigen entwickelt haben, deren Reste uns in den Versteinerungen erhalten sind. Nun ergibt sich aus den Vorgängen der künstlichen Züchtung, daß wirklich eine Form in eine andere sich verwandeln kann. Es entsteht nur die Frage, wodurch werden in der Natur selbst die Bedingungen zu dieser Umwandlung geschaffen, die der Züchter auf künstlichem Wege herbeiführt?
[ 7 ] Bei der künstlichen Züchtung wählt die menschliche Intelligenz die Bedingungen so, daß die neuentstehenden Formen dem Zwecke angepaßt sind, den der Züchter verfolgt. Nun sind aber auch die in der Natur lebenden organischen Formen im allgemeinen den Bedingungen zweckmäßig angepaßt, unter denen sie leben. Jeder Blick in die Natur kann über die Wahrheit dieser Tatsache belehren. Die Tier- und Pflanzenspezies sind so eingerichtet, daß sie in den Verhältnissen, in denen sie leben, sich erhalten und fortpflanzen können.
[ 8 ] Diese zweckmäßige Einrichtung ist es eben, welche das Vorurteil hervorgerufen hat, daß die organischen Formen sich nicht auf dieselbe Weise erklären lassen wie die Tatsachen der leblosen Natur. Kant führt in der «Kritik der Urteilskraft» aus: «Die Analogie der Formen, sofern sie bei aller Verschiedenheit einem gemeinschaftlichen Urbilde gemäß erzeugt zu sein scheinen, verstärkt die Vermutung einer wirklichen Verwandtschaft derselben in der Erzeugung von einer gemeinschaftlichen Urmutter durch stufenweise Annäherung einer Tiergattung zur andern... Hier steht nun dem Archäologen der Natur frei, aus den übriggebliebenen Spuren ihrer ältesten Revolutionen, nach allem ihm bekannten und gemutmaßten Mechanismus derselben, jene große Familie von Geschöpfen (denn so müßte man sie sich vorstellen, wenn die genannte durchgängig zusammenhängende Verwandtschaft einen Grund haben soll) entspringen zu lassen... Allein er muß gleichwohl zu dem Ende dieser allgemeinen Mutter eine auf alle diese Geschöpfe zweckmäßig gestellte Organisation beilegen, widrigenfalls die Zweckform der Produkte des Tier- und Pflanzenreichs ihrer Möglichkeit nach gar nicht zu denken ist.»
[ 9 ] Will man die organischen Formen in derselben Art erklären, wie die Naturwissenschaft es mit den unorganischen Erscheinungen macht, so muß gezeigt werden, daß die zweckmäßige Einrichtung der Organismen ohne einen absichtlich in sie gelegten Zweck gerade so naturnotwendig entsteht, wie eine elastische Kugel gesetzmäßig dahinrollt, wenn sie von einer andern gestoßen wird. Diese Forderung hat Darwin durch seine Lehre von der natürlichen Zuchtwahl erfüllt. Gemäß ihrer durch die künstliche Züchtung erwiesenen Verwandlungsfähigkeit müssen sich die organischen Formen auch in der Natur umbilden. Ist nichts vorhanden, was von vorneherein die Verwandlung so einrichtet, daß nur zweckmäßige Formen entstehen, so werden wahllos unzweckmäßige oder mehr oder weniger zweckmäßige entstehen. Nun ist die Natur ungeheuer verschwenderisch in der Hervorbringung ihrer Keime. Auf unserer Erde werden so viele Keime erzeugt, daß sich in kurzer Zeit eine große Anzahl Welten füllen könnten, wenn sie alle zur Entwickelung kämen. Dieser großen Zahl von Keimen steht nur ein verhältnismäßig geringes Maß von Nahrung und Raum gegenüber. Die Folge davon ist ein allgemeiner Kampf ums Dasein unter den organischen Wesen. Nur die Tüchtigen werden sich erhalten und fortpflanzen können; die Untüchtigen müssen zugrunde gehen. Die Tüchtigsten werden aber eben die sein, die den Lebensbedingungen am zweckmäßigsten angepaßt sind. Der durchaus absichtslose und naturnotwendige Kampf ums Dasein bewirkt somit dasselbe, was die Intelligenz des Züchters mit den Kulturorganismen vollbringt: er schafft zweckmäßige organische Formen. Dies ist in großen Umrissen der Sinn der von Darwin aufgestellten Lehre von der natürlichen Zuchtwahl im Kampf ums Dasein oder der Selektionstheorie. Durch sie war erreicht, was Kant für unmöglich gehalten hat: die Zweckform der Produkte des Tier- und Pflanzenreichs ihrer Möglichkeit nach zu denken, ohne der allgemeinen Mutter eine auf alle diese Geschöpfe zweckmäßig gestellte Organisation beizulegen.
[ 10 ] Wie Newton durch seine Lehre von der allgemeinen Anziehung der Himmelskörper zeigte, warum diese in den von Kopernikus und Kepler festgestellten Bahnen sich bewegen, so konnte man nunmehr mit Hilfe der Selektionstheorie erklären, wie sich in der Natur die Entwickelung des Lebendigen vollzieht, deren Gang Goethe in «Zur Morphologie» mit den Worten bezeichnet hat: «So viel aber können wir sagen, daß die aus einer kaum zu sondernden Verwandtschaft als Pflanzen und Tiere nach und nach hervortretenden Geschöpfe nach zwei entgegengesetzten Seiten sich vervollkommnen, so daß die Pflanze sich zuletzt im Baum dauernd und starr, das Tier im Menschen zur höchsten Beweglichkeit und Freiheit sich verherrlicht.» Goethe hat von seinem Verfahren gesagt: «Ich raste nicht, bis ich einen prägnanten Punkt finde, von dem sich vieles ableiten läßt, oder vielmehr der vieles freiwillig aus sich hervorbringt und mir entgegenträgt.» Für Ernst Haeckel wurde die Selektionstheorie der Punkt, aus dem er eine ganze naturwissenschaftliche Weltanschauung ableitete.
[ 11 ] Auch Jean Lamarck hat bereits im Anfange unseres Jahrhunderts die Ansicht vertreten, daß zu einer gewissen Zeit in der Erdentwickelung sich aus den mechanischen, physikalischen und chemischen Prozessen heraus durch Urzeugung ein einfachstes Organisches entwickelt habe. Diese einfachsten Organismen haben dann vollkommenere erzeugt und diese wieder höher organisierte bis herauf zum Menschen. «Man könnte daher diesen Teil der Entwicklungstheorie, welcher die gemeinsame Abstammung aller Tier- und Pflanzenarten von einfachsten gemeinsamen Stammformen behauptet, seinem verdientesten Begründer zu Ehren mit vollem Rechte Lamarckismus nennen.» Haeckel hat im großen Stile eine Erklärung des Lamarckismus durch den Darwinismus gegeben.
[ 12 ] Den Schlüssel zu dieser Erklärung fand Haeckel dadurch, daß er in der individuellen Entwickelung der höheren Organismen in ihrer Ontogenie — die Zeugnisse dafür suchte, daß sie wirklich von niederen Lebewesen abstammen. Wenn man die Formentwikkelung eines höheren Organismus vom ersten Keime bis zum ausgebildeten Zustande verfolgt, so stellen die verschiedenen Stufen Gestalten dar, welche den Formen niederer Organismen entsprechen.2Biogenetisches Grundgesetz. Haeckel hat die allgemeine Geltung und weittragende Bedeutung des biogenetischen Grundgesetzes in einer Reihe von Arbeiten nachgewiesen. Die wichtigsten Aufschlüsse und Beweise findet man in seiner «Biologie der Kalkschwämme» (1872) und in seinen «Studien zur Gasträa-Theorie»s (1873-84). Seitdem haben diese Lehre andere Zoologen ausgebaut und bestätigt. In seiner neuesten Schrift «Die Welträtsel» (1899) kann Haeckel von ihr sagen (S. 72): «Obgleich dieselbe anfangs fast allgemein abgelehnt und während eines Dezenniums von zahlreichen Autoritäten heftig bekämpft wurde, ist sie doch gegenwärtig (seit etwa fünfzehn Jahren) von allen sachkundigen Fachgenossen angenommen.» Im Beginne seiner individuellen Existenz ist der Mensch und jedes andere Tier eine einfache Zelle. Diese teilt sich, und aus ihr entsteht eine aus vielen Zellen bestehende Keimblase. Aus ihr entwickelt sich der sogenannte Becherkeim, die zweischichtige Gastrula, die die Gestalt eines becherförmigen oder krugförmigen Körpers hat. Nun bleiben die niederen Pflanzentiere (Spongien, Polypen und so weiter) während ihres ganzen Lebens auf einer Entwickelungsstufe stehen, welche diesem Becherkeim gleicht. Haeckel sagt darüber: «Diese Tatsache ist von außerordentlicher Bedeutung. Denn wir sehen, daß der Mensch, und überhaupt jedes Wirbeltier, rasch vorübergehend ein zweiblättriges Bildungsstadium durchläuft, welches bei jenen niedersten Pflanzentieren zeitlebens erhalten bleibt.» (Anthropogenie S.175.) Ein solcher Parallelismus zwischen den Entwickelungsstadien der höheren Organismen und den ausgebildeten niederen Formen läßt sich durch die ganze individuelle Entwickelungsgeschichte hindurch verfolgen. Haeckel kleidet diese Tatsache in die Worte: «Die kurze Ontogenese oder die Entwicklung des Individuums ist eine schnelle und zusammengezogene Wiederholung, eine gedrängte Rekapitulation der langen Phylogenese oder der Entwicklung der Art.» Dieser Satz drückt das sogenannte biogenetische Grundgesetz aus. Wodurch kommen nun die höheren Organismen im Lauf ihrer Entwickelung zu Formen, die den niederen gleichen? Die naturgemäße Erklärung ist die, daß sich jene aus diesen entwickelt haben, daß also jeder Organismus in seiner individuellen Entwickelung uns die Gestalten aufeinanderfolgend zeigt, die ihm als Erbstück von seinen niederen Vorfahren geblieben sind.
[ 13 ] Der einfachste Organismus, der sich dereinst auf der Erde gebildet hat, verwandelt sich im Laufe der Fortpflanzung in neue Formen. Von diesen bleiben die bestangepaßten im Kampf ums Dasein übrig und vererben ihre Eigenschaften auf ihre Nachkommen. Alle Gestaltungen und Eigenschaften, die ein Organismus gegenwärtig zeigt, sind in großen Zeiträumen durch Anpassung und Vererbung entstanden. Die Vererbung und die Anpassung sind also die Ursachen der organischen Formenwelt.
[ 14 ] Haeckel hat also dadurch, daß er das Verhältnis der individuellen Entwickelungsgeschichte (Ontogenie) zur Stammesgeschichte (Phylogenie) suchte, die naturwissenschaftliche Erklärung der mannigfaltigen organischen Formen gegeben.3Haeckels neueste Schrift. In seinem kürzlich erschienenen Buche «Die Welträtsel, Gemeinverständliche Studien über monistische Philosophie» (Bonn, Emil Strauß, 1899) hat Haeckel rückhaltlos die «weitere Ausführung, Begründung und Ergänzung der Überzeugungen» gegeben, die er in den oben angeführten Schriften bereits ein Menschenalter hindurch vertreten hat. Demjenigen, der die naturwissenschaftlichen Erkenntnisse unserer Zeit in sich aufgenommen hat, muß dieses Werk als eines der bedeutendsten Manifeste vom Ende des neunzehnten Jahrhunderts erscheinen. Es enthält in reifer Form eine vollständige Auseinandersetzung der modernen Naturwissenschaft mit dem philosophischen Denken aus dem Geiste des genialsten, weitblickendsten Naturforschers unserer Zeit heraus. Er hat als Naturphilosoph die menschliche Erkenntnisforderung erfüllt, die Schiller aus der Beobachtung des Goetheschen Geistes gewonnen hat: er ist aufgestiegen von der einfachen Organisation, Schritt vor Schritt, zu der mehr verwickelten, um endlich die verwickeltste von allen, den Menschen, genetisch aus den Materialien des ganzen Naturgebäudes zu erbauen. Seine Ansicht hat er in mehreren großangelegten Werken niedergelegt, in seiner «Generellen Morphologie der Organismen» (1866), in der «Natürlichen Schöpfungsgeschichte» (1868), in der «Anthropogenie» (1874), in der er «den ersten und bis jetzt einzigen Versuch unternommen hat, den zoologischen Stammbaum des Menschen im einzelnen kritisch zu begründen und die ganze tierische Ahnenreihe unseres Geschlechts... eingehend zu erörtern». Zu diesen Werken ist in den letzten Jahren (1894-1896) noch seine dreibändige «Systematische Phylogenie» getreten.
[ 15 ] Es ist bezeichnend für die tiefe philosophische Natur Haeckels, daß er nach dem Erscheinen von Darwins «Entstehung der Arten» (1859) sogleich die volle Tragweite der darin aufgestellten Grundsätze für die gesamte Weltanschauung des Menschen erkannte; und es spricht für seinen philosophischen Enthusiasmus, daß er mit Kühnheit unermüdlich alle die Vorurteile bekämpfte, die sich gegen die Aufnahme der neuen Wahrheit in das Glaubensbekenntnis des modernen Geistes erhoben. Die Notwendigkeit, daß alles moderne wissenschaftliche Denken mit dem Darwinismus zu rechnen hat, setzte Haeckel in der fünfzigsten Versammlung deutscher Naturforscher und Ärzte am 18. September 1877 in dem Vortrage über «Die heutige Entwicklungslehre im Verhältnisse zur Gesamtwissenschaft» auseinander. Ein umfassendes «Glaubensbekenntnis eines Naturforschers» trug er am 9. Oktober 1892 in Altenburg beim 75jährigen Jubiläum der naturforschenden Gesellschaft des Osterlandes vor. (Gedruckt ist diese Rede unter dem Titel «Der Monismus als Band zwischen Religion und Wissenschaft», Bonn 1892.) Was sich aus der reformierten Entwickelungslehre und aus unserem gegenwärtigen naturwissenschaftlichen Wissen für die Beantwortung der «Frage aller Fragen» ergibt, hat er in großen Linien kürzlich in dem oben erwähnten Vortrage «Über unsere gegenwärtige Kenntnis vom Ursprung des Menschen» entwickelt. Hier behandelt Haeckel neuerdings die Konsequenz, die sich für jeden logisch Denkenden ohne weiteres aus dem Darwinismus ergibt, daß der Mensch sich aus niederen Wirbeltieren, und zwar zunächst aus echten Affen, entwickelt hat. Dieser notwendige Folgeschluß ist es aber auch gewesen, welcher alle alten Vorurteile der Theologen, Philosophen und aller, die in deren Bann stehen, zum Kampf gegen die Entwickelungstheorie aufgerufen hat. Zweifelsohne hätte man sich ein Hervorgehen der einzelnen Tier- und Pflanzenformen auseinander gefallen lassen, wenn dessen Annahme nur nicht zugleich auch die Anerkennung der tierischen Abstammung des Menschen nach sich gezogen hätte. «Es bleibt», wie Haeckel in seiner «Natürlichen Schöpfungsgeschichte» betonte, «eine lehrreiche Tatsache, daß diese Anerkennung keineswegs» — nach dem Erscheinen des ersten Darwinschen Werkes — «allgemein war, daß vielmehr zahlreiche Kritiker des ersten’ Darwinschen Buches (und darunter sehr berühmte Namen) sich vollkommen mit dem Darwinismus einverstanden erklärten, aber jede Anwendung desselben auf den Menschen gänzlich von der Hand wiesen.» Mit einem gewissen Schein von Recht berief man sich dabei auf Darwins Buch selbst, in dem von dieser Anwendung kein Wort steht. Haeckel wurde deswegen, weil er rücksichtslos diese unabweisliche Konsequenz zog, der Vorwurf gemacht, daß er «darwinistischer als Darwin selbst sei». Das ging freilich nur bis zum Jahre 1871, in dem Darwins Werk erschien «Die Abstammung des Menschen und die geschlechtliche Zuchtwahl». Hier vertritt dieser selbst mit großer Kühnheit und Klarheit diese Folgerung.
[ 16 ] Man erkannte richtig, daß mit dieser Folgerung eine Vorstellung fallen muß, die zu den geschätztesten in der Sammlung älterer menschlicher Vorurteile gehört: diejenige, daß die «Seele des Menschen» ein besonderes Wesen für sich sein soll, das einen ganz anderen «höheren Ursprung» habe als alle anderen Naturdinge. Die Abstammungslehre muß natürlich zu der Ansicht führen, daß die seelischen Tätigkeiten des Menschen nur eine besondere Form derjenigen physiologischen Funktionen sind, die sich bei dessen Wirbeltier-Ahnen finden, und daß diese Tätigkeiten sich mit eben derselben Notwendigkeit aus den Geistestätigkeiten der Tiere entwickelt haben, wie sich das Gehirn des Menschen, welches die materielle Bedingung des Geistes ist, aus dem Wirbeltiergehirn entwickelt hat.
[ 17 ] Nicht nur die Menschen mit alten, durch die verschiedenen Kirchenreligionen großgezogenen Glaubensvorstellungen sträubten sich gegen das neue Bekenntnis, sondern auch alle diejenigen, die sich zwar scheinbar von diesen Glaubensvorstellungen freigemacht haben, deren Geist aber doch noch immer im Sinne dieser Vorstellungen denkt. In dem Folgenden soll der Nachweis geführt werden, daß zu der letzteren Art von Geistern eine Reihe von Philosophen und naturwissenschaftlich hochstehenden Gelehrten gehört, die Haeckel bekämpft haben und noch immer Gegner der von ihm vertretenen Ansichten sind. Zu ihnen gesellen sich dann die, welchen überhaupt die Fähigkeit abgeht, aus einer Reihe vorliegender Tatsachen die notwendigen logischen Folgerungen zu ziehen. Welches die Einwände sind, gegen die Haeckel seinen Kampf zu führen hatte, möchte ich hier zur Darstellung bringen.
II
[ 18 ] Auf die Verwandtschaft des Menschen mit den höheren Wirbeltieren wirft die Wahrheit ein helles Licht, die Huxley 1863 in seinen «Zeugnissen für die Stellung des Menschen in der Natur» ausgesprochen hat: «Die kritische Vergleichung aller Organe und ihrer Modifikationen innerhalb der Affen-Reihe führt uns zu einem und demselben Resultate: Die anatomischen Verschiedenheiten, welche den Menschen vom Gorilla und Schimpansen scheiden, sind nicht so groß als die Unterschiede, welche diese Menschenaffen von den niedrigeren Affen trennen.» Mit Hilfe dieser Tatsache ist es möglich, die tierische Ahnenreihe des Menschen im Sinne der Darwinschen Abstammungslehre festzustellen. Der Mensch hat mit den Ostaffen zusammen gemeinsame Stammeltern in einer ausgestorbenen Affenart. Durch entsprechende Benutzung der Erkenntnisse, welche vergleichende Anatomie und Physiologie, individuelle Entwickelungsgeschichte und Paläontologie liefern, hat Haeckel die in der Zeit weiter vorausliegenden tierischen Vorfahren des Menschen, über die Halbaffen, Beuteltiere, Urfische bis hinauf zu den Urdarmtieren und den nur aus einer Zelle bestehenden Urtieren verfolgt. Er hat ein volles Recht zu dem Ausspruche: Sind die Erscheinungen der individuellen Entwickelung des Menschen etwa weniger wunderbar als die paläontologische Entwickelung aus niederen Organismen? Warum soll der Mensch sich nicht im Laufe großer Zeiträume aus einzelligen Urformen entwickelt haben, da jedes Individuum dieselbe Entwickelung von der Zelle zum ausgebildeten Organismus durchläuft?
[ 19 ] Es wird dem menschlichen Geist aber auch nicht leicht, sich über die Entwickelung des Einzelorganismus vom Keim bis zum ausgebildeten Zustand naturgemäße Vorstellungen zu bilden. Wir sehen das an den Gedanken, die sich ein Naturforscher wie Albrecht von Haller und ein Philosoph wie Leibniz über diese Entwickelung gebildet haben. Haller vertrat die Ansicht, daß der Keim eines Organismus bereits alle Teile, die während der Entwickelung auftreten, im kleinen, aber vollkommen fertig vorgebildet enthalte. Entwickelung soll also nicht Bildung eines Neuen an dem Vorhandenen sein, sondern Auswickelung eines schon Dagewesenen und wegen seiner Kleinheit nur dem Auge Verborgenen. Wäre diese Ansicht richtig, dann müßten aber auch in dem ersten Keim einer tierischen oder pflanzlichen Form alle folgenden Generationen bereits ineinander eingeschachtelt gelegen haben. Haller hat diese Folgerung auch gezogen. Er nahm an, daß in dem ersten Menschenkeim der Urmutter Eva das ganze Menschengeschlecht im kleinen bereits vorhanden gewesen ist. Und auch Leibniz kann sich die Entstehung der Menschen nur als Auswickelung von bereits Existierendem denken: «So sollte ich meinen, daß die Seelen, welche eines Tages menschliche Seelen sein werden, im Samen wie jene von anderen Spezies dagewesen sind, daß sie in den Voreltern bis auf Adam, also seit dem Anfang der Dinge, immer in der Form organisierter Körper existiert haben.»
[ 20 ] Der menschliche Verstand hat einen Hang sich vorzustellen, daß etwas Entstehendes schon in irgendeiner Form vor der Entstehung vorhanden gewesen ist. Der ganze Organismus soll schon im Keim verborgen sein; die einzelnen organischen Klassen, Ordnungen, Familien, Gattungen und Arten sollen als Gedanken eines Schöpfers vor ihrer tatsächlichen Entstehung vorhanden sein. Nun fordert aber die Idee der Entwickelung, daß wir uns die Entstehung eines Neuen, Späteren aus einem bereits Vorhandenen, Früheren vorstellen. Wir sollen das Gewordene aus dem Werden begreifen. Das können wir nicht, wenn wir alles Gewordene als ein immer Dagewesenes ansehen.
[ 21 ] Wie groß die Vorurteile sind, die der Entwickelungsidee entgegengebracht werden, das zeigte sich deutlich an der Aufnahme, die Caspar Friedrich Wolffs 1759 erschienene «Theoria generationis» bei den zu Hallers Ansichten sich bekennenden Narurforschern fand. In dieser Schrift wurde gezeigt, daß im menschlichen Ei noch nicht eine Spur von der Form des ausgebildeten Organismus vorhanden ist, sondern daß dessen Entwickelung in einer Kette von Neubildungen besteht. Wolff verteidigte die Idee einer wirklichen Entwickelung, der Epigenesis, eines Werdens von noch nicht Vorhandenem, gegenüber der Ansicht von der scheinbaren Entwickelung, der Einschachtelung und Auswickelung. Haeckel sagt von Wolffs Schrift, sie «gehört trotz ihres geringen Umfanges und ihrer schwerfälligen Sprache zu den wertvollsten Schriften im ganzen Gebiete der biologischen Literatur...» Trotzdem hatte diese merkwürdige Schrift zunächst gar keinen Erfolg. Obgleich die naturwissenschaftlichen Studien infolge der von Linné gegebenen Anregung zu jener Zeit mächtig emporblühten, obgleich Botaniker und Zoologen bald nicht mehr nach Dutzenden, sondern nach Hunderten zählten, bekümmerte sich doch niemand um Wolffs Theorie der Generation. Die wenigen aber, die sie gelesen hatten, hielten sie für grundfalsch, so besonders Haller. Obgleich Wolff durch die exaktesten Beobachtungen die Wahrheit der Epigenesis bewies und die in der Luft schwebenden Hypothesen der Präformationstheorie widerlegte, blieb dennoch der «exakte» Physiologe Haller der eifrigste Anhänger der letzteren und verwarf die richtige Lehre von Wolff mit seinem diktatorischen Machtspruche: «Es gibt kein Werden» (Nulla est epigenesis!). Mit solcher Macht widersetzte sich das Denken einer Ansicht, von der Haeckel (in seiner «Anthropogenie») findet: «Wir können heutzutage diese Theorie der Epigenesis kaum mehr Theorie nennen, weil wir uns von der Richtigkeit der Tatsache völlig überzeugt haben und dieselbe jeden Augenblick mit Hilfe des Mikroskopes demonstrieren können.»
[ 22 ] Wie tief eingewurzelt das Vorurteil gegen die Idee der Entwickelung ist, darüber können uns die Einwände, die unsere philosophischen Zeitgenossen gegen sie machen, jeden Augenblick belehren. Otto Liebmann, der wiederholt, in seiner «Analysis der Wirklichkeit» und in «Gedanken und Tatsachen», die naturwissenschaftlichen Grundansichten einer Kritik unterworfen hat, äußert sich über den Entwickelungsgedanken in einer merkwürdigen Weise. Er kann die Berechtigung der Vorstellung, daß höhere Organismen aus niederen hervorgehen, angesichts der Tatsachen nicht leugnen. Deshalb versucht er die Tragweite dieser Vorstellung als eine für das höhere Erklärungsbedürfnis möglichst geringe hinzustellen. «Angenommen, Deszendenztheorie ... wäre fertig, der große Stammbaum der organischen Naturwesen läge offen vor uns aufgerollt; und zwar nicht als Hypothese, sondern als historisch-konstatiertes Faktum, was hätten wir dann? Eine Ahnengallerie, wie man sie auf fürstlichen Schlössern auch findet; nur nicht als Fragment, sondern als abgeschlossene Totalität.» Es soll also für die wirkliche Erklärung nichts Erhebliches getan sein, wenn man zeigt, wie das Spätere als Neubildung aus dem Früheren hervorgeht. Es ist nun interessant, zu sehen, wie Liebmanns Voraussetzungen ihn doch wieder zu der Annahme hinführen, das auf dem Wege der Entwickelung Entstehende sei schon vor seiner Entstehung vorhanden. In dem vor kurzem erschienenen zweiten Heft seiner «Gedanken und Tatsachen» behauptet er: «Für uns freilich, denen die Welt in der Anschauungsform der Zeit erscheint, ist der Same früher da als die Pflanze, Erzeugung und Empfängnis früher da als das daraus entspringende Tier, und die Entwickelung des Embryo zum erwachsenen Geschöpf ein in der Zeit ablaufender, zeitlich in die Länge gezogener Prozeß. In dem zeitlosen Weltwesen hingegen, welches nicht entsteht und nicht vergeht, sondern ein für alle Male ist, sich im Strome des Geschehens unabänderlich erhält, und für welches keine Zukunft, keine Vergangenheit, sondern nur eine ewige Gegenwart existiert, fällt dieses Vorher und Nachher, dieses Früher und Später gänzlich hinweg... Das, was sich für uns in der Linie der Zeit als langsamer oder schneller ablaufende Sukzession einer Reihe von Entwicklungsphasen entrollt, ist im allgegenwärtigen, permanenten Weltwesen ein feststehendes, unentstandenes und unvergängliches Gesetz.» Der Zusammenhang solcher philosophischen Vorstellungen mit den Auffassungen der verschiedenen Religionslehren über die Schöpfung ist leicht einzusehen. Daß in der Natur zweckmäßig eingerichtete Wesen entstehen, ohne eine zugrunde liegende Tätigkeit oder Kraft, welche die Zweckmäßigkeit in die Wesen hineinlegt, wollen weder die Religionslehren noch solche philosophische Denker wie Liebmann zugeben. Die narurgemäße Anschauung verfolgt den Gang des Geschehens und sieht Wesen entstehen, welche die Eigenschaft der Zweckmäßigkeit haben, ohne daß der Zweck selbst mitbestimmend bei ihrer Entstehung gewesen ist. Die Zweckmäßigkeit ist mit ihnen geworden, aber der Zweck hat bei diesem Werden nicht mitgewirkt.4Es wird von denjenigen, die gerne gläubig an dem Vorhandensein von Zwecken in der Natur festhalten möchten, immer wieder betont, daß Darwins Anschauungen den Zweckgedanken doch nicht beseitigten, sondern ihn erst recht benutzen, indem sie zeigen, wie die Verkettung von Ursachen und Wirkungen durch sich selbst notwendig zur Entstehung des Zweckmäßigen führen müsse. Es kommt aber nicht darauf an, ob man das Vorhandensein von zweckmäßigen Bildungen in der Natur zugibt oder nicht, sondern ob man annimmt oder ablehnt, daß der Zweck, das Ziel als Ursache bei Entstehung dieser Bildungen mitwirkt. Wer diese Annahme macht, der vertritt die Teleologie oder Zweckmäßigkeitslehre. Wer dagegen sagt: der Zweck ist in keiner Weise bei der Entstehung der organischen Welt tätig; die Lebewesen entstehen nach notwendigen Gesetzen wie die unorganischen Erscheinungen, und die Zweckmäßigkeit ist nur da, weil das Unzweckmäßige sich nicht erhalten kann; sie ist nicht der Grund der Vorgänge, sondern deren Folge: der bekennt sich zum Darwinismus. Das beachtet nicht, wer wie Otto Liebmann behauptet: «Einer der größten Teleologen der Gegenwart ist Charles Darwin» (Gedanken und Tatsachen, 1. Heft, S. 113). Nein, er ist der größte Antiteleologe, weil er solchen Geistern wie Liebmann, wenn sie ihn verstünden, zeigen würde, daß das Zweckgemäße erklärt werden kann, ohne daß man die Tätigkeit von wirkenden Zwecken voraussetzt. Die religiöse Vorstellungsart greift zu dem Schöpfer, der nach dem vorgefaßten Plane die Geschöpfe zweckmäßig geschaffen hat; Liebmann wendet sich an ein zeitloses Weltwesen, aber er läßt das Zweckmäßige doch durch den Zweck hervorgebracht sein. «Das Ziel oder der Zweck ist hier nicht später und auch nicht früher als das Mittel, sondern er fordert es vermöge einer zeitlosen Norwendigkeit.» Liebmann ist ein gutes Beispiel für die Philosophen, die sich scheinbar von Glaubensvorstellungen freigemacht haben, die aber doch ganz im Sinne solcher Vorstellungen denken. Sie wollen ihre Gedanken rein aus vernünftigen Erwägungen heraus bestimmen lassen; die Richtung gibt ihnen aber doch ein eingeimpftes theologisches Vorurteil.
[ 23 ] Ein vernunftgemäßes Nachdenken muß daher Haeckel beipflichten, wenn er sagt: «Entweder haben sich die Organismen natürlich entwickelt, und dann müssen sie alle von einfachsten, gemeinsamen Stammformen abstammen — oder das ist nicht der Fall, die einzelnen Arten der Organismen sind unabhängig voneinander entstanden, und dann können sie nur auf übernatürlichem Wege durch ein Wunder erschaffen sein. Natürliche Entwicklung oder übernatürliche Schöpfung der Arten —, zwischen diesen beiden Möglichkeiten ist zu wählen, ein Drittes gibt es nicht!» Was von Philosophen oder Naturforschern gegenüber der natürlichen Entwickelungslehre als solches Drittes vorgebracht wird, erweist sich bei genauerer Betrachtung nur als ein seinen Ursprung mehr oder weniger verschleiernder oder verleugnender Schöpfungsglaube.
[ 24 ] Wenn wir die Frage nach der Entstehung der Arten in ihrer wichtigsten Form aufwerfen, in der nach dem Ursprung des Menschen, so gibt es nur zwei Antworten. Entweder ist ein vernunftbegabtes Bewußtsein vor seinem tatsächlichen Auftreten in der Welt in keiner Weise vorhanden, sondern es entsteht als Ergebnis des im Gehirn konzentrierten Nervensystems, oder eine alles beherrschende Weltvernunft existiert vor allen übrigen Wesen und gestaltet den Stoff so, daß im Menschen ihr Abbild zur Erscheinung kommt. Haeckel stellt (in «Der Monismus als Band zwischen Religion und Wissenschaft») das Werden des Menschengeistes in folgender Weise dar: «Wie unser menschlicher Körper sich langsam und stufenweise aus einer langen Reihe von Wirbeltierahnen herangebildet hat, so gilt dasselbe auch von unserer Seele; als Funktion unseres Gehirns hat sie sich stufenweise in Wechselwirkung mit diesem ihrem Organ entwickelt. Was wir kurzweg «menschliche Seele» nennen, ist ja nur die Summe unseres Empfindens, Wollens und Denkens, die Summe von physiologischen Funktionen, deren Elementarorgane die mikroskopischen Ganglienzellen unseres Gehirns bilden. Wie der bewunderungswürdige Bau dieses letzteren, unseres menschlichen Seelenorgans, sich im Laufe von Jahrmillionen allmählich aus den Gehirnformen höherer und niederer Wirbeltiere emporgebildet hat, zeigt uns die vergleichende Anatomie und Ontogenie; wie Hand in Hand damit auch die Seele selbst — als Funktion des Gehirns — sich entwickelt hat, das lehrt uns die vergleichende Psychologie. Die letztere zeigt uns auch, wie eine niedere Form der Seelentätigkeit schon bei den niedersten Tieren vorhanden ist, bei den einzelligen Urtieren, Infusorien und Rhizopoden. Jeder Naturforscher, der gleich mir lange Jahre hindurch die Lebenstätigkeit dieser einzelligen Protisten beobachtet hat, ist positiv überzeugt, daß auch sie eine Seele besitzen; auch diese «Zellseele» besteht aus einer Summe von Empfindungen, Vorstellungen und Willenstätigkeiten; das Empfinden, Denken und Wollen unserer menschlichen Seele ist nur stufenweise davon verschieden.» Die Gesamtheit menschlicher Seelentätigkeiten, die in dem einheitlichen Selbstbewußisein ihren höchsten Ausdruck findet, entspricht dem komplizierten Bau des menschlichen Gehirnes ebenso wie das einfache Empfinden und Wollen der Organisation des Urtieres.5In neuester Zeit ist es Paul Flechsig gelungen, nachzuweisen, daß in einem Teile der Denkorgane des Menschen sich verwickelte Strukturen finden, die bei den übrigen Säugetieren nicht vorhanden sind. Sie vermitteln offenbar diejenigen geistigen Tätigkeiten, durch die der Mensch sich vom Tiere unterscheidet. Die Fortschritte der Physiologie, die wir Forschern wie Goltz, Munk, Wernicke, Edinger, Paul Flechsig und anderen verdanken, geben uns heute die Möglichkeit, einzelne Seelenäußerungen bestimmten Teilen des Gehirnes als deren besondere Funktionen zuzuweisen. Wir sehen in vier Gebieten der grauen Rindenzone des Hirnmantels die Vermittler von vier Arten des Empfindens: die Körperfühlsphäre im Scheitellappen, die Riechsphäre im Stirnlappen, die Sehsphäre im Hinterhauptlappen, die Hörsphäre im Schläfenlappen. Das die Empfindungen verbindende und ordnende Denken hat seine Werkzeuge zwischen diesen vier «Sinnesherden». Haeckel knüpft an die Erörterung dieser neueren physiologischen Ergebnisse die Bemerkung: «Die vier Denkherde, durch eigentümliche und höchst verwickelte Nervenstruktur vor den zwischenliegenden Sinnesherden ausgezeichnet, sind die wahren ‹Denkorgane›, die einzigen realen Werkzeuge unseres Geisteslebens» (Über unsere gegenwärtige Kenntnis vom Ursprung des Menschen).
[ 25 ] Haeckel fordert von den Psychologen, daß sie solche Ergebnisse bei ihren Ausführungen über das Wesen der Seele berücksichtigen und nicht eine Scheinwissenschaft aufbauen, die sich zusammensetzt aus phantastischer Metaphysik, einseitiger, sogenannter innerer Beobachtung der Seelenvorgänge, unkritischer Vergleichung, mißverstandenen Wahrnehmungen und unvollständigen Erfahrungen aus spekulativen Verirrungen und religiösen Dogmen. Man findet dem Vorwurf gegenüber, der durch diese Ansicht der veralteten Seelenkunde gemacht wird, bei Philosophen und auch bei einzelnen Naturforschern die Behauptung, daß in den materiellen Vorgängen des Gehirnes doch nicht das eingeschlossen sein könne, was wir als Geist zusammenfassen; die stofflichen Vorgänge in den Sinnes- und Denksphären seien doch keine Vorstellungen, Empfindungen und Gedanken, sondern nur materielle Erscheinungen. Das Wesen der Gedanken und Empfindungen könnten wir nicht durch äußere Beobachtung, sondern nur durch innere Erfahrung, durch rein geistige Selbstbeobachtung kennenlernen. Gustav Bunge zum Beispiel führt in einem Vortrage «Vitalismus und Mechanismus» (Seite 12) aus: «In der Aktivität — da steckt das Rätsel des Lebens darin. Den Begriff der Aktivität aber haben wir nicht aus der Sinneswahrnehmung geschöpft, sondern aus der Selbstbeobachtung, aus der Beobachtung des Willens, wie er in unser Bewußtsein tritt, wie er dem inneren Sinn sich offenbart.» Manche Denker sehen das Kennzeichen eines philosophischen Kopfes in der Fähigkeit, sich zu der Einsicht zu erheben, daß es eine Umkehrung des richtigen Verhältnisses der Dinge ist, die geistigen Vorgänge aus materiellen begreifen zu wollen.
[ 26 ] Solche Einwände deuten auf ein Mißverständnis der, von Haeckel vertretenen Weltanschauung hin. Wer wirklich von dem Sinn dieser Weltanschauung durchdrungen ist, wird die Gesetze des geistigen Lebens niemals auf einem anderen Wege als durch innere Erfahrung, durch Selbstbeobachtung zu erforschen suchen. Die Gegner der naturwissenschaftlichen Denkungsart reden gerade so, als wenn deren Anhänger die Wahrheiten der Logik, Ethik, Ästhetik und so weiter nicht durch Beobachtung der Geisteserscheinungen als solcher, sondern aus den Ergebnissen der Gehirnanatomie gewinnen wollten. Das von solchen Gegnern selbstgeschaffene Zerrbild naturwissenschaftlicher Weltanschauung nennen sie dann Materialismus und werden nicht müde, immer von neuem zu wiederholen, daß diese Ansicht unfruchtbar sein muß, weil sie die geistige Seite des Daseins ignoriere oder wenigstens auf Kosten der materiellen herabsetze. Otto Liebmann, der hier noch einmal angeführt werden mag, weil seine antinaturwissenschaftlichen Vorstellungen typisch für die Denkweise gewisser Philosophen und Laien sind, bemerkt: «Gesetzt nun aber, die Naturerkenntnis wäre ans Ziel gelangt, so würde sie in der Lage sein, mir genau die körperlich-organischen Gründe anzugeben, weshalb ich den Satz zweimal zwei ist vie für wahr halte und behaupte, den anderen Satz «zweimal zwei ist fünf für falsch halte und bestreite, oder weshalb ich diese Zeilen hier gerade jetzt aufs Papier schreiben muß, während ich in dem subjektiven Glauben befangen bin, es geschehe dies deshalb, weil ich sie wegen ihrer von mir angenommenen Wahrheit niederschreiben will» (Gedanken und Tatsachen). Kein naturwissenschaftlicher Denker wird je der Meinung sein, daß darüber, was im logischen Sinne wahr oder falsch ist, die körperlich-organischen Gründe Aufschluß geben können. Die geistigen Zusammenhänge können nur aus dem geistigen Leben heraus erkannt werden. Was logisch berechtigt ist, darüber wird immer die Logik, was künstlerisch vollkommen ist, darüber wird das ästhetische Urteil entscheiden. Ein anderes aber ist die Frage: Wie entsteht das logische Denken, wie das ästhetische Urteil als Funktion des Gehirnes? Über diese Frage allein spricht sich die vergleichende Physiologie und Gehirnanatomie aus. Und diese zeigen, daß das vernünftige Bewußtsein nicht für sich abgesondert existiert und das menschliche Gehirn nur benutzt, um sich durch dasselbe zu äußern, wie der Klavierspieler auf dem Klavier spielt, sondern daß unsere Geisteskräfte ebenso Funktionen der FormElemente unseres Gehirns sind, wie «jede Kraft die Funktion eines materiellen Körpers ist» (Haeckel, Anthropogenie).
[ 27 ] Das Wesen des Monismus besteht in der Annahme, daß alle Weltvorgänge, von den einfachsten mechanischen an bis herauf zu den höchsten menschlichen Geistesschöpfungen, in gleichem Sinne sich naturgemäß entwickeln und daß alles, was zur Erklärung der Erscheinungen herangezogen wird, innerhalb der Welt selbst zu suchen ist. Dieser Anschauung steht der Dualismus gegenüber, der die reine Naturgesetzlichkeit nicht für ausreichend hält, um die Erscheinungen zu erklären, sondern zu einer über den Erscheinungen waltenden, vernünftigen Wesenheit seine Zuflucht nimmt. Diesen Dualismus muß die Naturwissenschaft, wie gezeigt worden ist, verwerfen.
[ 28 ] Es wird nun von seiten der Philosophie geltend gemacht, daß die Mittel der Naturwissenschaft nicht ausreichen, um eine Weltanschauung zu begründen. Von ihrem Standpunkte aus hätte die Naturwissenschaft ganz recht, wenn sie den ganzen Weltprozeß als eine Kette von Ursachen und Wirkungen im Sinne einer rein mechanischen Gesetzmäßigkeit erklärt; aber hinter dieser Gesetzmäßigkeit stecke doch die eigentliche Ursache, die allgemeine Weltvernunft, die sich der mechanischen Mittel nur bedient, um höhere, zweckmäßige Zusammenhänge zu verwirklichen. So sagt zum Beispiel der in den Bahnen Eduard von Hartmanns wandelnde Arthur Drews: «Auch das menschliche Kunstwerk kommt auf mechanische Weise zustande, wenn man nämlich nur die äußerliche Aufeinanderfolge der einzelnen Momente dabei im Auge hat, ohne darauf zu reflektieren, daß hinter diesem allem doch nur der Gedanke des Künstlers steckt; dennoch würde man denjenigen mit Recht für einen Narren halten, der etwa behaupten wollte, das Kunstwerk sei rein mechanisch entstanden ...., was sich auf jenem niedrigeren, mit der bloßen Anschauung der Wirkung sich begnügenden Standpunkte, der also den ganzen Prozeß gleichsam nur von hinten betrachtet, als gesetzmäßige Wirkung einer Ursache darstellt, dasselbe erweist sich, von vorne gesehen, allemal als beabsichtigter Zweck des angewandten Mittels» (Die deutsche Spekulation seit Kant). Und Eduard von Hartmann selbst sagt von dem Kampf ums Dasein, der es ermöglicht, die Lebewesen naturgemäß zu erklären: «Der Kampf ums Dasein und mit ihm die ganze natürliche Zuchtwahl ist nur ein Handlanger der Idee, der die niederen Dienste bei der Verwirklichung jener, nämlich das Behauen und Anpassen der vom Baumeister nach ihrem Platz im großen Bauwerk bemessenen und typisch vorherbestimmten Steine, verrichten muß. Diese Auslese im Kampf ums Dasein für das im wesentlichen zureichende Erklärungsprinzip der Entwickelung des organischen Reiches ausgeben, wäre nicht anders, als wenn ein Tagelöhner, der beim Zurichten der Steine beim Kölner Dombau mitgewirkt, sich für den Baumeister dieses Kunstwerkes erklären wollte» (Philosophie des Unbewußten).
[ 29 ] Wären diese Vorstellungen berechtigt, so käme es der Philosophie zu, den Künstler hinter dem Kunstwerke zu suchen. Philosophen haben in der Tat die verschiedensten dualistischen Erklärungsweisen der Welterscheinungen versucht. Sie haben in Gedanken gewisse Wesenheiten konstruiert, die hinter den Erscheinungen schweben sollen, wie der Künstlergeist hinter dem Kunstwerke waltet.
[ 30 ] Alle naturwissenschaftlichen Betrachtungen könnten dem Menschen die Überzeugung nicht nehmen, daß die wahrnehmbaren Erscheinungen von außerweltlichen Wesen gelenkt werden, wenn er innerhalb seines Geistes selbst etwas fände, was auf solche Wesen hindeutet. Was vermöchten Anatomie und Physiologie mit ihrer Erklärung, daß die Seelentätigkeiten Funktionen des Gehirnes sind, wenn die Beobachtung dieser Tätigkeiten etwas lieferte, was als höherer Erklärungsgrund anzusehen ist? Wenn der Philosoph uns zu zeigen vermöchte, daß sich in der menschlichen Vernunft eine allgemeine Weltvernunft offenbart, dann könnten eine solche Erkenntnis alle naturwissenschaftlichen Ergebnisse nicht widerlegen.
[ 31 ] Nun wird aber die dualistische Weltanschauung durch nichts besser widerlegt als durch die Betrachtung des menschlichen Geistes. Wenn ich einen äußeren Vorgang, zum Beispiel die Bewegung einer elastischen Kugel, die durch eine andere gestoßen worden ist, erklären will, so kann ich nicht bei der bloßen Beobachtung stehen bleiben, sondern ich muß das Gesetz suchen, das Bewegungsrichtung und Schnelligkeit der einen Kugel durch Richtung und Schnelligkeit der anderen bestimmt. Ein solches Gesetz kann mir nicht die bloße Beobachtung, sondern nur die gedankliche Verknüpfung der Vorgänge liefern. Der Mensch entnimmt also aus seinem Geiste die Mittel, um das zu erklären, was sich ihm durch die Beobachtung darbietet. Er muß über die Beobachtung hinausgehen, wenn er sie begreifen will. Beobachtung und Denken sind die beiden Quellen unserer Erkenntnisse über die Dinge. Das gilt für alle Dinge und Vorgänge, nur nicht für das denkende Bewußtsein selbst. Ihm können wir durch keine Erklärung etwas hinzufügen, was nicht schon in der Beobachtung liegt. Es liefert uns die Gesetze für alles andere, es liefert uns zugleich auch seine eigenen. Wenn wir die Richtigkeit eines Naturgesetzes dartun wollen, so vollbringen wir dies dadurch, daß wir Beobachtungen, Wahrnehmungen unterscheiden, ordnen, Schlüsse ziehen, also uns Begriffe und Ideen über die Erfahrungen mit Hilfe des Denkens bilden. Über die Richtigkeit des Denkens entscheidet nur das Denken selbst. So ist es das Denken, das uns bei allem Weltgeschehen über die bloße Beobachtung, nicht aber über sich selbst hinausführt.
[ 32 ] Diese Tatsache ist unvereinbar mit der dualistischen Weltanschauung. Was die Anhänger dieser Weltanschauung so oft betonen, daß die Äußerungen des denkenden Bewußtseins uns durch den inneren Sinn der Selbstbeobachtung zugänglich sind, während wir das physische, das chemische Geschehen nur begreifen, wenn wir die Tatsachen der Beobachtung durch logische, mathematische Kombination und so weiter, also durch die Ergebnisse der geisteswissenschaftlichen Gebiete, in die entsprechenden Zusammenhänge bringen: das dürften sie vielmehr niemals zugeben. Denn man ziehe nur einmal die richtige Folgerung aus der Erkenntnis, daß Beobachtung in Selbstbeobachtung umschlägt, wenn wir aus naturwissenschaftlichem in geisteswissenschaftliches Gebiet heraufgehen. Läge den Naturerscheinungen eine allgemeine Weltvernunft oder ein anderes geistiges Urwesen zugrunde (zum Beispiel Schopenhauers Wille oder Hartmanns unbewußter Geist), so müßte auch der denkende Menschengeist von diesem Weltwesen geschaffen sein. Eine Übereinstimmung der Begriffe und Ideen, die sich dieser Geist von den Erscheinungen bildet, mit der eigenen Gesetzmäßigkeit dieser Erscheinungen wäre nur möglich, wenn der ideelle Weltkünstler in der menschlichen Seele die Gesetze erzeugte, nach denen er vorher die ganze Welt geschaffen hat. Dann aber könnte der Mensch seine eigene geistige Tätigkeit nicht durch Selbstbeobachtung, sondern durch Beobachtung des Urwesens erkennen, von dem er gebildet ist. Es gäbe eben keine Selbstbeobachtung, sondern nur Beobachtung der Absichten und Zwecke des Urwesens. Mathematik und Logik zum Beispiel dürften nicht dadurch ausgebildet werden, daß der Mensch die innere, eigene Natur geistiger Zusammenhänge sucht, sondern daß er diese geisteswissenschaftlichen Wahrheiten aus den Absichten und Zwecken der ewigen Weltvernunft ableitet. Wäre die menschliche Vernunft nur Abbild einer ewigen, dann könnte sie ihre Gesetzmäßigkeit nimmermehr durch Selbstbeobachtung gewinnen, sondern sie müßte sie aus der ewigen Vernunft heraus erklären. Wo immer aber eine solche Erklärung versucht worden ist, ist stets einfach die menschliche Vernunft in die Welt hinaus versetzt worden. Wenn der Mystiker durch Versenken in sein Inneres sich zur Anschauung Gottes zu erheben glaubt, so sieht er in Wirklichkeit nur seinen eigenen Geist, den er zum Gott macht, und wenn Eduard von Hartmann von Ideen spricht, die sich der Naturgesetze als Handlanger bedienen, um den Weltenbau zu bilden, so sind diese Ideen nur seine eigenen, durch die er sich die Welt erklärt. Weil Beobachtung der Geistesäußerungen Selbstbeobachtung ist, deshalb spricht sich im Geiste das eigene Selbst und nicht eine äußere Vernunft aus.
[ 33 ] Im vollen Einklange mit der Tatsache der Selbstbeobachtung steht aber die monistische Entwickelungslehre. Hat sich die menschliche Seele langsam und stufenweise mit den Seelenorganen aus niederen Zuständen entwickelt, so ist es selbstverständlich, daß wir ihr Entstehen von unten her naturwissenschaftlich erklären, daß wir aber die innere Wesenheit dessen, was sich zuletzt aus dem komplizierten Bau des menschlichen Gehirns ergibt, nur durch die Betrachtung dieser Wesenheit selbst gewinnen können. Wäre Geist in einer der menschlichen Form ähnlichen immer vorhanden gewesen und hätte sich zuletzt nur im Menschen sein Gegenbild geschaffen, so müßten wir den Menschengeist aus dem Allgeist ableiten können; ist aber der Menschengeist im Laufe der natürlichen Entwickelung als Neubildung entstanden, dann begreifen wir sein Herkommen, wenn wir seine Ahnenreihe verfolgen; wir lernen die Stufe, zu der er zuletzt gekommen ist, kennen, wenn wir ihn selbst betrachten.
[ 34 ] Eine sich selbst verstehende und auf unbefangene Betrachtung des menschlichen Geistes gerichtete Philosophie liefert also einen weiteren Beweis für die Richtigkeit der monistischen Weltanschauung. Sie ist dagegen ganz unverträglich mit einer dualistischen Naturwissenschaft. (Die weitere Ausführung und ausführliche Begründung einer monistischen Philosophie, deren Grundgedanken ich hier nur andeuten konnte, habe ich in meiner «Philosophie der Freiheit» gegeben.)
[ 35 ] Wer die monistische Weltanschauung recht versteht, für den verlieren auch alle Einwendungen, die ihr von der Ethik gemacht werden, alle Bedeutung. Haeckel hat wiederholt auf das Unberechtigte solcher Einwendungen hingewiesen und auch darauf aufmerksam gemacht, wie die Behauptung, daß der naturwissenschaftliche Monismus zum sittlichen Materialismus führen müsse, entweder auf einer vollkommenen Verkennung des ersteren beruht, oder aber auf eine bloße Verdächtigung desselben hinausläuft.
[ 36 ] Der Monismus sieht natürlich das menschliche Handeln nur als einen Teil des allgemeinen Weltgeschehens an.66Das Verdienst, gezeigt zu haben, daß kein wirklicher Gegensatz zwischen Tierund Menschenseele besteht, sondern daß in einer naturgemäßen Entwickelungsreihe sich die Geistestätigkeiten des Menschen an die der Tiere als eine höhere Form derselben anschließen, gebührt George John Romanes, der in einem umfassenden Werke: «Die geistige Entwicklung im Tierreich» (1. Band, Leipzig 1885) und «Die geistige Entwicklung beim Menschen. Ursprung der menschlichen Fähigkeiten» (2. Band, Leipzig 1893) gezeigt hat, «daß die psychologische Schranke zwischen Tier und Mensch überwunden ist». Er macht es ebensowenig abhängig von einer sogenannten höheren moralischen Weltordnung, wie er das Naturgeschehen von einer übernatürlichen Ordnung abhängig sein läßt. «Die mechanische oder monistische Philosophie behauptet, daß überall in den Erscheinungen des menschlichen Lebens, wie in denen der übrigen Natur, feste und unabänderliche Gesetze walten, daß überall ein notwendiger ursächlicher Zusammenhang, ein Kausalnexus der Erscheinungen besteht und daß demgemäß die ganze uns erkennbare Welt ein einheitliches Ganzes, ein «Monon», bildet. Sie behauptet ferner, daß alle Erscheinungen nur durch mechanische Ursachen, nicht durch vorbedachte zwecktätige Ursachen hervorgebracht werden. Einen «freien Willen» im gewöhnlichen Sinne gibt es nicht. Vielmehr erscheinen im Lichte der monistischen Weltanschauung auch diejenigen Erscheinungen, die wir als die freiesten und unabhängigsten zu betrachten uns gewöhnt haben, die Äußerungen des menschlichen Willens, gerade so festen Gesetzen unterworfen wie jede andere Naturerscheinung» (Haeckel, Anthropogenie). Die monistische Philosophie zeigt die Erscheinung des freien Willens erst im rechten Lichte. Als Ausschnitt des allgemeinen Weltgeschehens steht der menschliche Wille unter denselben Gesetzen wie alle anderen natürlichen Dinge und Vorgänge. Er ist naturgesetzlich bedingt. Indem aber die monistische Ansicht leugnet, daß in dem Naturgeschehen höhere, zwecktätige Ursachen vorhanden sind, erklärt sie zugleich auch den Willen unabhängig von einer solchen höheren Weltordnung. Der natürliche Entwickelungsprozeß führt die Naturvorgänge herauf bis zum menschlichen Selbstbewußtsein. Auf dieser Stufe überläßt er den Menschen sich selbst, dieser kann nunmehr die Antriebe seiner Handlungen aus seinem eigenen Geiste holen. Waltete eine allgemeine Weltvernunft, so könnte der Mensch auch seine Ziele nicht aus sich, sondern nur aus dieser ewigen Vernunft holen. Im Sinne des Monismus ist hiernach das Handeln des Menschen durch ursächliche Momente bestimmt; im ethischen Sinne ist es nicht bestimmt, weil die ganze Natur nicht ethisch, sondern naturgesetzlich bestimmt ist. Die Vorstufen des sittlichen Handelns sind bereits bei niederen Organismen vorhanden. «Wenn auch später beim Menschen die moralischen Fundamente sich viel höher entwickelten, so liegt doch ihre älteste, prähistorische Quelle, wie Darwin gezeigt hat, in den sozialen Instinkten der Tiere» (Haeckel, Monismus). Das sittliche Handeln des Menschen ist ein Entwickelungsprodukt. Der sittliche Instinkt der Tiere vervollkommnet sich wie alles andere in der Natur durch Vererbung und Anpassung, bis der Mensch aus seinem eigenen Geiste heraus sich sittliche Zwecke und Ziele setzt. Nicht als vorherbestimmt durch eine übernatürliche Weltordnung, sondern als Neubildung innerhalb des Naturprozesses erscheinen die sittlichen Ziele. In sittlicher Beziehung «zweckvoll ist nur dasjenige, was der Mensch erst dazu gemacht hat, denn nur durch Verwirklichung einer Idee entsteht Zweckmäßiges. Wirksam im realistischen Sinne wird die Idee aber nur im Menschen... Auf die Frage: Was hat der Mensch für eine Aufgabe im Leben, kann der Monismus nur antworten: die, die er sich selbst setzt. Meine Sendung in der Welt ist keine (ethisch) vorherbestimmte, sondern sie ist jeweilig die, die ich mir erwähle. Ich trete nicht mit gebundener Marschroute meinen Lebensweg an» (vergleiche meine «Philosophie der Freiheit», XI: Weltzweck und Lebenszweck). Der Dualismus fordert Unterwerfung unter die von irgendwoher geholten sittlichen Gebote. Der Monismus weist den Menschen auf sich selbst. Dieser empfängt von keinem äußeren Weltwesen sittliche Maßstäbe, sondern nur aus seiner eigenen Wesenheit heraus. Die Fähigkeit, sich selbst ethische Zwecke zu schaffen, kann man moralische Phantasie nennen. Der Mensch erhebt durch sie die ethischen Instinkte seiner niederen Vorfahren zum moralischen Handeln, wie er durch die künstlerische Phantasie die Gestalten und Vorgänge der Natur in seinen Kunstwerken auf einer höheren Stufe widerspiegelt.
[ 37 ] Die philosophischen Erwägungen, die sich aus dem Vorhandensein der Selbstbeobachtung ergeben, sind somit keine Widerlegung, sondern eine wichtige Ergänzung der aus der vergleichenden Anatomie und Physiologie genommenen Beweismittel der monistischen Weltanschauung.
III
[ 38 ] Eine absonderliche Stellung der monistischen Weltanschauung gegenüber nimmt der berühmte Pathologe Rudolf Virchow ein.6Das Verdienst, gezeigt zu haben, daß kein wirklicher Gegensatz zwischen Tierund Menschenseele besteht, sondern daß in einer naturgemäßen Entwickelungsreihe sich die Geistestätigkeiten des Menschen an die der Tiere als eine höhere Form derselben anschließen, gebührt George John Romanes, der in einem umfassenden Werke: «Die geistige Entwicklung im Tierreich» (1. Band, Leipzig 1885) und «Die geistige Entwicklung beim Menschen. Ursprung der menschlichen Fähigkeiten» (2. Band, Leipzig 1893) gezeigt hat, «daß die psychologische Schranke zwischen Tier und Mensch überwunden ist». Nachdem Haeckel auf der fünfzigsten Versammlung deutscher Naturforscher und Ärzte seinen Vortrag über «Die heutige Entwicklungslehre im Verhältnisse zur Gesamtwissenschaft» gehalten, in dem er geistvoll die Bedeutung der monistischen Weltanschauung für unsere geistige Kultur und auch für das Untertichtswesen dargelegt hatte, trat vier Tage später Virchow in derselben Versammlung als sein Gegner mit der Rede auf: «Die Freiheit der Wissenschaft im modernen Staat.». Zunächst schien es, als ob Virchow den Monismus nur aus der Schule verbannt wissen wollte, weil nach seiner Ansicht die neue Lehre bloß eine Hypothese sei und nicht eine durch sichere Beweise belegte Tatsache darstelle. Merkwürdig erscheint es allerdings, wenn ein moderner Naturforscher die Entwickelungslehre angeblich aus Mangel an unumstößlichen Beweisen aus dem Unterrichte verbannen will und zugleich dem Dogma der Kirche das Wort redet. Sagt doch Virchow (auf Seite 29 der genannten Rede): «Jeder Versuch, unsere Probleme zu Lehrsätzen umzubilden, unsere Vermutungen als die Grundlagen des Unterrichts einzuführen, der Versuch insbesondere, die Kirche einfach zu depossedieren und ihr Dogma ohne weiteres durch eine Deszendenz-Religion zu ersetzen, ja, meine Herren, dieser Versuch muß scheitern, und er wird in seinem Scheitern zugleich die höchsten Gefahren für die Stellung der Wissenschaft überhaupt mit sich führen!» Man muß da doch die jedem vernünftigen Denken gegenüber bedeutungslose Frage aufwerfen: Gibt es denn für die kirchlichen Dogmen sicherere Beweise als für die «Deszendenz-Religion»? Aus der ganzen Art, wie Virchow damals gesprochen hat, ergibt sich aber, daß es sich ihm weniger um die Abwendung der Gefahren, die der Monismus dem Unterricht bringen könnte, handelt, als vielmehr um seine prinzipielle Gegnerschaft zu dieser Weltanschauung überhaupt. Das hat er durch sein ganzes seitheriges Verhalten bewiesen. Er hat jede ihm passend erscheinende Gelegenheit ergriffen, um die natürliche Entwickelungsgeschichte zu bekämpfen und seinen Lieblingssatz zu wiederholen: «Es ist ganz gewiß, daß der Mensch nicht vom Affen abstammt.» Beim fünfundzwanzigjährigen Stiftungsfest der «Deutschen Anthropologischen Gesellschaft», am 24. August 1894, kleidete er sogar diesen Satz in die wenig geschmackvollen Worte: «Auf dem Wege der Spekulation ist man zu der Affentheorie gekommen; man hätte ebensogut ... zu einer Elefantentheorie oder einer Schaftheorie kommen können.» Dieser Ausspruch hat natürlich gegenüber den Ergebnissen der vergleichenden Zoologie nicht den geringsten Sinn. «Kein Zoologe» — bemerkt Haeckel — «wird es für möglich halten, daß der Mensch vom Elefanten oder vom Schafe abstammen könne. Denn gerade diese beiden Säugetiere gehören zu den spezialisiertesten Zweigen der Huftiere, einer Ordnung der Säugetiere, die mit derjenigen der Affen oder Primaten in gar keinem direkten Zusammenhange steht (ausgenommen die gemeinsame Abstammung von einer ursprünglichen Stammesform der ganzen Klasse).» — So schwer es dem verdienstvollen Naturforscher gegenüber wird: man kann derlei Aussprüche nur als leere Redensarten bezeichnen.7Am 3. Oktober 1898 hielt Virchow die zweite der «Huxley Lectures» in der Charing Cross Hospital Medical School zu London, in der er sagte: «Ich darf annehmen, daß mir ein solcher Auftrag nicht erteilt worden wäre, wenn die Auftraggeber nicht gewußt hätten, wie tief das Gefühl der Verehrung für Huxley in meiner Seele ist, wenn sie nicht gesehen hätten, wie ich von den ersten bahnbrechenden Publikationen des verstorbenen Meisters an seine Leistungen anerkannt und wie sehr ich die Freundschaft geschätzt habe, die er mir persönlich zuteil werden ließ.» Nun bedeuten gerade diese bahnbrechenden Publikationen Huxleys den ersten großen Schritt zur Ausbildung der Theorie von der Affenabstammung des Menschen, die Virchow bekämpft und über die er auch in dem Huxley-Vortrag «Die neueren Fortschritte in der Wissenschaft» nichts zu sagen weiß als einige gegenüber dem heutigen Stande der Frage ganz bedeutungslose Worte, wie: «Man mag über die Enistehung des Menschen denken, wie man will, die Überzeugung von der prinzipiellen Übereinstimmung der menschlichen und der tierischen Organisation ist gegenwärtig allgemein angenommen... und so weiter.» Virchow befolgt bei seiner Bekämpfung der Deszendenztheorie eine ganz eigentümliche Taktik. Er fordert unumstößliche Beweise für diese Theorie. Sobald aber die Naturwissenschaft irgend etwas findet, was die Kette der Beweise um ein neues Glied zu bereichern in der Lage ist, dann sucht er dessen Beweiskraft in jeder Weise zu entkräften. Die Deszendenztheorie sieht in den berühmten Schädeln von Neanderthal, von Spy und so weiter vereinzelte paläontologische Überreste von ausgestorbenen niederen Menschen-Rassen, welche zwischen dem affenartigen Vorfahren des Menschen (Pithecanthropus) und den niederen Menschen-Rassen der Gegenwart ein Übergangsglied bilden. Virchow erklärt diese Schädel für abnorme, krankhafte Bildungen, für pathologische Produkte. Er bildete sogar diese Behauptung dahin aus, daß alle Abweichungen von den einmal feststehenden organischen Urformen solche pathologische Gebilde seien. Wenn wir also durch künstliche Züchtung aus wildem Obst Tafelobst hervorbringen, so haben wir nur ein krankes Naturobjekt erzeugt. Man kann den Virchowschen aller Entwickelungstheorie feindlichen Satz: «Der Plan der Organisation ist innerhalb der Spezies unveränderlich, Art läßt nicht von Art» nicht bequemer beweisen, als wenn man das, was vor unseren Augen zeigt, wie Art von Art läßt, nicht als gesundes, naturgemäßes Entwickelungsprodukt, sondern als krankes Gebilde erklärt. Ganz entsprechend diesem Verhalten Virchows zur Abstammungslehre waren auch seine Behauptungen über die Knochenreste des Menschenaffen (Pithecanthropus erectus), die Eugen Dubois 1894 in Java gefunden hat. Allerdings waren diese Überreste, ein Schädeldach, ein Oberschenkel und einige Zähne, unvollständig. Über sie entspann sich auf dem Zoologen-Kongreß in Leiden [1895] eine Debatte, die höchst interessant war. Von zwölf Zoologen waren drei der Ansicht, daß die Reste von einem Affen, drei, daß sie von einem Menschen stammen, sechs vertraten die Meinung, daß man es mit einer 'ausgestorbenen Übergangsform zwischen Mensch und Affe zu tun habe. Dubois hat in einleuchtender Weise das Verhältnis dieses Mittelgliedes zwischen Mensch und Affe einerseits zu den niederen Rassen des Menschengeschlechts, anderseits zu den bekannten Menschenaffen dargelegt. Virchow erklärte, daß der Schädel und der Oberschenkel nicht zusammengehören, sondern daß der erstere von einem Affen, der letztere von einem Menschen herrühre. Diese Behauptung wurde von sachkundigen Paläontologen widerlegt, die auf Grund des gewissenhaften Fundberichtes sich dahin aussprachen, daß nicht der geringste Zweifel bestehen könne über die Herkunft der Knochenreste von einem und demselben Individuum. Daß der Oberschenkel nur von einem Menschen herrühren könne, suchte Virchow durch eine Knochenwucherung an demselben zu beweisen, die von einer nur durch sorgsame menschliche Pflege zur Heilung gebrachten Krankheit herrühren müsse. Dagegen zeigte der Paläontologe Marsh, daß ähnliche Knochenauswüchse auch bei wilden Affen vorkommen. Eine dritte Behauptung Virchows, daß die tiefe Einschnürung zwischen dem Oberrand der Augenhöhlen und dem niederen Schädeldach des Pithecanthropus für dessen Affennatur spreche, konnte der Paläontologe Nehring damit zurückweisen, daß sich dieselbe Bildung an einem Menschenschädel von Santos in Brasilien findet.
[ 39 ] Virchows Kampf gegen die Entwickelungslehre erscheint in der Tat rätselhaft, wenn man bedenkt, daß dieser Forscher im Beginne seiner wissenschaftlichen Laufbahn, vor der Veröffentlichung von Darwins «Entstehung der Arten» 118591, die Lehre von den mechanischen Grundlagen aller Lebenstätigkeit vertrat. In Würzburg, wo Virchow von 1848-1856 lehrte, saß Haeckel «andachtsvoll zu seinen Füßen und vernahm zuerst von ihm mit Enthusiasmus jene klare und einfache Lehre». Die durch Darwin geschaffene Umwandlungslehre, die ein umfassendes Erklärungsprinzip für diese Lehre liefert, bekämpft aber Virchow. Wenn er gegenüber den Tatsachen der Versteinerungskunde, der vergleichenden Anatomie und Physiologie fortwährend betont, daß die «sicheren Beweise» fehlen, so kann demgegenüber nur geltend gemacht werden, daß zur Anerkennung der Entwickelungslehre allerdings die Kenntnis der Tatsachen nicht ausreicht, sondern daß dazu — wie Haeckel sagt — auch «ein philosophisches Verständnis» derselben gehört. Es «entsteht nur durch die innigste Wechselwirkung und gegenseitige Durchdringung von Erfahrung und Philosophie das unerschütterliche Gebäude der wahren monistischen Wissenschaft» (Haeckel, Natürliche Schöpfungsgeschichte). Gefährlicher als all die Schäden, die eine «Deszendenz-Religion» in unreifen Köpfen anrichten kann, ist jedenfalls Virchows seit Jahrzehnten unter dem Beifall der theologischen und anderer Reaktionäre geführter Kampf gegen die Abstammungslehre. Eine sachliche Auseinandersetzung mit Virchow wird dadurch erschwert, daß er im Grunde bei der bloßen Verneinung stehenbleibt und sachliche Einwände gegen die Entwickelungslehre im allgemeinen nicht vorbringt.
[ 40 ] Andere naturwissenschaftliche Gegner Haeckels machen es uns leichter, über sie zur Klarheit zu gelangen, weil sie die Gründe für ihre Gegnerschaft angeben und wir daher die Fehler in ihren Folgerungen einsehen können. Zu ihnen sind Wilhelm His und Alexander Goette zu zählen.
[ 41 ] His trat im Jahre 1868 mit seinen «Untersuchungen über die erste Anlage des Wirbeltierleibes» auf. Sein Kampf richtet sich vor allen Dingen gegen die Lehre, daß die Formentwickelung eines höheren Organismus vom ersten Keim bis zum ausgebildeten Zustande ihre Erklärung durch die Stammesentwickelung finde. Nicht dadurch sollen wir diese Entwickelung erklären, daß wir sie als Resultat der durch Vererbung und Anpassung vermittelten Entwickelung der Generationen hinstellen, von denen der Einzelorganismus abstammt, sondern wir sollen, ohne Rücksicht auf vergleichende Anatomie und Stammesgeschichte, in dem Einzelorganismus selbst die mechanischen Ursachen seines Werdens suchen. His geht davon aus, daß der als gleichartige Fläche gedachte Keim an verschiedenen Stellen ungleich wächst, und behauptet, daß infolge dieses ungleichen Wachstums im Laufe der Entwickelung der komplizierte Bau des Organismus hervorgehe. Er sagt: man nehme eine einfache Platte und stelle sich vor, daß sie an verschiedenen Stellen einen verschiedenen Antrieb zur Vergrößerung besitze. Dann wird man aus rein mathematischen und mechanischen Gesetzen den Zustand entwickeln können, in dem sich das Gebilde nach einiger Zeit befinden muß. Seine aufeinanderfolgenden Formen werden genau den Entwickelungsstadien entsprechen, die der Einzelorganismus vom Keim bis zum vollkommenen Zustande durchläuft, So brauchen wir also nicht über die Betrachtung des Einzelorganismus hinauszugehen, um seine Entwickelung zu begreifen, sondern wir können diese aus dem mechanischen Wachstumsgesetz selbst ableiten. «Alle Formung, bestehe sie in Blätterspaltung, in Faltenbildung oder in vollständiger Abgliederung, geht als eine Folge aus jenem Grundgesetz hervor.» Die beiden Gliedmaßenpaare bringt das Wachstumsgesetz auf folgende Weise zustande: «Ihre Anlage wird, den vier Ecken eines Briefes ähnlich, durch die Kreuzung von vier den Körper umgrenzenden Falten bestimmt.» His weist die Zuhilfenahme der Stammesgeschichte mit der Begründung ab: «Hat die Entwicklungsgeschichte für eine gegebene Form die Aufgabe physiologischer Ableitung durchgreifend erfüllt, dann darf sie mit Recht von sich sagen, daß sie diese Form als Einzelform erklärt habe.» In Wirklichkeit ist aber mit einer solchen Erklärung gar nichts getan. Denn es fragt sich doch: warum wirken an verschiedenen Stellen des Keimes verschiedene Wachstumskräfte. Sie werden von His einfach als vorhanden angenommen. Die Erklärung kann nur darin gesehen werden, daß die Wachstumsverhältnisse der einzelnen Teile des Keimes von den Ahnentieren durch Vererbung übertragen sind, daß somit der Einzelorganismus die aufeinanderfolgenden Stufen seiner Entwickelung durchläuft, weil die Veränderungen, die seine Vorfahren in großen Zeiträumen erfahren haben, als Ursache seines individuellen Werdens nachwirken.
[ 42 ] Zu welchen Konsequenzen die Anschauung von His führt, zeigt sich am besten an seiner «Höhlenlappen-Theorie». Durch sie sollen die sogenannten «rudimentären Organe» des Organismus erklärt werden. Es sind dies Teile, die am Organismus vorhanden sind, ohne daß sie für das Leben desselben irgendwelche Bedeutung haben. So hat der Mensch am inneren Winkel seines Auges eine Haurfalte, die für die Verrichtungen seines Sehorgans ohne jeden Zweck ist. Er hat auch die Muskeln, welche denen entsprechen, durch die gewisse Tiere ihre Ohren willkürlich bewegen können. Dennoch können die meisten Menschen ihre Ohren nicht bewegen. Manche Tiere besitzen Augen, die von einer Haut bedeckt sind, also nicht zum Sehen dienen können. His erklärt diese Organe als solche, denen «bis jetzt keine physiologische Rolle sich hat zuteilen lassen, ... den Abfällen vergleichbar, welche beim Zuschneiden eines Kleides auch bei der sparsamsten Verwendung des Stoffes sich nicht völlig vermeiden lassen». Die Entwickelungstheorie gibt für sie die einzig mögliche Erklärung. Sie sind von den Voreltern ererbt. Bei diesen hatten sie ihren guten Zweck. Tiere, die heute unter der Erde leben und nicht sehende Augen haben, stammen von solchen Ahnen ab, die im Lichte lebten und Augen brauchten. Im Laufe vieler Generationen haben sich die Lebensverhältnisse eines solchen organischen Stammes geändert. Die Lebewesen haben sich den neuen Verhältnissen angepaßt, in denen ihnen die Sehorgane entbehrlich sind. Aber diese sind als Erbstücke aus einer früheren Entwickelungsstufe geblieben, nur sind sie im Laufe der Zeit verkümmert, weil sie nicht gebraucht wurden. Diese rudimentären Organe 8Über diese Organe sagt Haeckel in seinem Buche «Die Welträtsel»,. 306: «Alle höheren Tiere und Pflanzen, überhaupt alle diejenigen Organismen, deren Körper nicht ganz einfach gebaut, sondern aus mehreren, zweckmäßig zusammenwirkenden Organen zusammengesetzt ist, lassen bei aufmerksamer Untersuchung eine Anzahl von nutzlosen oder unwirksamen, ja zum Teil sogar gefährlichen und schädlichen Einrichtungen erkennen... Die Erklärung dieser zwecklosen Einrichtungen finden wir sehr einfach durch die Deszendenztheorie. Sie zeigt, daß diese rudimentären Organe verkümmert sind, und zwar durch Nichtgebrauch.... Der blinde Kampf ums Dasein zwischen den Organen bedingt ebenso ihren historischen Untergang, wie er ursprünglich ihre Entstehung und Ausbildung verursachte.» sind eines der stärksten Beweismittel für die natürliche Entwickelungstheorie. Wenn beim Aufbau einer organischen Form irgendwelche zwecksetzende Absichten geherrscht hätten: woher kämen diese unzweckmäßigen Teile? Es gibt für sie keine andere mögliche Erklärung, als daß sie im Laufe vieler Generationen allmählich außer Gebrauch gekommen sind.
[ 43 ] Auch Alexander Goette ist der Ansicht, daß man die Entwickelungsstadien des Einzelorganismus nicht auf dem Umwege durch die Stammesgeschichte zu erklären brauche. Er leitet die Gestaltung des Organismus von einem «Formgesetze» ab, das zu den physischen und chemischen Prozessen des Stoffes hinzutreten muß, um das Lebewesen zu bilden. Er suchte diesen Standpunkt ausführlich in seiner «Entwicklungsgeschichte der Unke» zu vertreten. «Das Wesen der Entwicklung besteht in der vollständigen, aber ganz allmählichen Einführung eines neuen, von außen bedingten Momentes, eben des Formgesetzes, in die Existenz gewisser Naturkörper.» Da das Formgesetz von außen zu den mechanischen und physikalischen Eigenschaften des Stoffes hinzutreten und nicht sich aus diesen Eigenschaften entwickeln soll, so kann es nichts anderes als eine stoffreie Idee sein, und wir haben ‘in ihm nichts gegeben, was sich im wesentlichen von den Schöpfungsgedanken unterscheidet, die nach der dualistischen Weltanschauung den organischen Formen zugrunde liegen. Es soll ein außer der organisierten Materie existierendes und deren Entwickelung verursachendes Motiv sein. Das heißt, es bedient sich der stofflichen Gesetze ebenso als Handlanger wie die Idee Eduard von Hartmanns. Goette muß dieses «Formgesetz» herbeirufen, weil er der Meinung ist, daß «die individuelle Entwicklungsgeschichte der Organismen» allein deren gesamte Gestaltung begründet und erklärt. Wer leugnet, daß die wahren Ursachen der Entwickelung des Einzelwesens ein historisches Ergebnis der Vorfahrenentwickelung sind, der wird notwendig zu solchen außer dem Stoffe liegenden ideellen Ursachen greifen müssen,
[ 44 ] Ein gewichtiges Zeugnis gegen solche Versuche, ideelle Gestaltungskräfte in die individuelle Entwickelungsgeschichte einzuführen, bieten die Leistungen solcher Naturforscher, welche die Gestaltungen höherer Lebewesen wirklich unter der Voraussetzung erklärt haben, daß diese Gestaltungen die erbliche Wiederholung von zahllosen stammesgeschichtlichen Veränderungen sind, die sich während langer Zeiträume abgespielt haben. Ein schlagendes Beispiel in dieser Hinsicht ist die schon von Goethe und Oken vorgeahnte, aber erst von Carl Gegenbaur auf Grund der Deszendenztheorie in das rechte Licht gerückte «Wirbeltheorie der Schädelknochen». Er führte den Nachweis, daß der Schädel der höheren Wirbeltiere und auch des Menschen durch allmähliche Umbildung eines Urschädels entstanden ist, dessen Form noch heute die Urfische oder Selachier in ihrer Kopfbildung bewahren. Gestützt auf solche Ergebnisse bemerkt daher Gegenbaur mit Recht: «An der vergleichenden Anatomie wird die Deszendenztheorie zugleich einen Prüfstein finden. Bisher besteht keine vergleichend-anatomische Erfahrung, die ihr widerspräche; vielmehr führen uns alle darauf hin. So wird jene Theorie das von der Wissenschaft zurückempfangen, was sie ihrer Methode gegeben hat: Klarheit und Sicherheit» (vergleiche die Einleitung zu Gegenbaurs: «Vergleichende Anatomie»). Die Deszendenztheorie hat die Wissenschaft darauf hingewiesen, die wirklichen Ursachen der individuellen Entwickelung des Einzelorganismus bei dessen Vorfahren zu suchen, und die Naturwissenschaft ersetzt auf diesem Wege alle ideellen Entwickelungsgesetze, die von irgendwo außerhalb an den organischen Stoff herantreten sollen, durch die tatsächlichen Vorgänge der Stammesgeschichte, die im Einzelwesen als Gestaltungskräfte fortwirken.
[ 45 ] Immer mehr nähert sich unter dem Einfluß der Deszendenztheorie die Naturwissenschaft dem großen Ziele, das einer der größten Naturforscher des Jahrhunderts, Karl Ernst von Baer, mit den Worten vorgezeichnet hat: «Ein Grundgedanke ist es, der durch alle Formen und Stufen der tierischen Entwicklung geht und alle einzelnen Verhältnisse beherrscht. Derselbe Grundgedanke ist es, der im Weltraum die verteilte Masse in Sphären sammelte und diese zu Sonnensystemen verband; derselbe, der den verwitterten Staub an der Oberfläche des Planeten in lebendige Formen hervorwachsen ließ. Dieser Gedanke ist aber nichts als das Leben selbst, und die Worte und Silben, in welchen er sich ausspricht, sind die verschiedenen Formen des Lebendigen.» Ein anderer Ausspruch Baers gibt dieselbe Vorstellung in anderer Form: «Noch manchem wird ein Preis zuteil werden. Die Palme aber wird der Glückliche erringen, dem es vorbehalten ist, die bildenden Kräfte des tierischen Körpers auf die allgemeinen Kräfte oder Lebensverrichtungen des Weltganzen zurückzuführen.»
[ 46 ] Es sind dieselben allgemeinen Naturkräfte, die den auf einer schiefen Ebene befindlichen Stein hinabrollen und die auch durch die Entwickelung aus einer organischen Form die andere entstehen lassen. Die Eigenschaften, die sich eine Form durch Generationen hindurch auf dem Wege der Anpassung erwirbt, die vererbt sie auf ihre Nachkommen. Was ein Lebewesen gegenwärtig von innen heraus aus seiner Keimesanlage entfaltet, das hat sich bei seinen Ahnen äußerlich im mechanischen Kampf mit den übrigen Naturkräften entwickelt. Um diese Ansicht festzuhalten, dazu ist allerdings notwendig, daß man annimmt, die in diesem äußeren Kampfe erworbenen Gestaltungen können sich wirklich vererben. Deshalb wird durch die namentlich von August Weismann verfochtene Meinung, daß sich erworbene Eigenschaften nicht vererben, die ganze Entwickelungslehre in Frage gestellt. Er ist der Ansicht, daß keine äußere Veränderung, die sich mit einem Organismus vollzogen hat, auf die Nachkommen übertragen werden kann, sondern daß sich nur dasjenige vererbt, was durch eine ursprüngliche Anlage des Keimes vorausbestimmt war. In den Keimen der Organismen sollen unzählige Entwickelungsmöglichkeiten liegen. Demnach können sich die organischen Formen im Laufe ihrer Fortpflanzung verändern. Eine neue Form entsteht, wenn in der Nachkommenschaft andere Entwickelungsmöglichkeiten zur Entfaltung kommen als bei den Vorfahren. Von den auf diese Weise immer neu entstehenden Formen werden sich diejenigen erhalten, die den Kampf ums Dasein am besten bestehen können. Formen, die diesem Kampfe nicht gewachsen sind, werden untergehen. Wenn sich aus einer Entwickelungsmöglichkeit eine Form bildet, die im Konkurrenzstreit besonders tüchtig ist, so wird diese Form sich fortpflanzen, wenn das nicht der Fall ist, muß sie untergehen. Man sieht, hier werden die äußerlich auf den Organismus wirkenden Ursachen ganz ausgeschaltet. Die Gründe, warum sich die Formen verändern, liegen im Keime. Und der Kampf ums Dasein wählt von den aus den verschiedensten Keimanlagen hervorgehenden Gestalten diejenigen aus, die am tauglichsten sind. Die Eigenschaft eines Organismus führt uns nicht hinauf zu einer Veränderung, die mit seinem Vorfahren vor sich gegangen ist, als zu deren Ursache, sondern zu einer Anlage im Keime dieses Vorfahren. Da also von außen nichts an dem Aufbau der organischen Formen bewirkt werden kann, so müssen im Keime der Urform, von der ein Stamm seine Entwickelung begonnen hat, schon die Anlagen für die folgenden Generationen liegen. Wir stehen wieder vor einer Einschachtelungslehre. Weismann denkt sich den fortschreitenden Prozeß, durch den die Keime die Entwickelung besorgen, als einen stofflichen Vorgang. Wenn ein Organismus entsteht, so wird von der Keimmasse, aus: der er sich entwickelt, ein Teil lediglich dazu verwendet, einen neuen Keim behufs weiterer Fortpflanzung zu bilden. In der Keimmasse eines Nachkommen ist also ein Teil derjenigen der Eltern vorhanden, in der Keimmasse der Eltern ein Teil derjenigen der Großeltern und so fort bis hinauf zu der Urform. Durch alle sich auseinander entwickelnden Organismen erhält sich also eine ursprünglich vorhandene Keimsubstanz. Dies ist Weismanns Theorie von der Kontinuität und Unsterblichkeit des Keimplasmas. Er glaubt sich zu dieser Anschauung gedrängt, weil ihm zahlreiche Tatsachen der Annahme einer Vererbung erworbener Eigenschaften zu widersprechen scheinen. Als eine besonders bemerkenswerte führt er das Vorhandensein der zur Fortpflanzung unfähigen Arbeiter bei den staatenbildenden Insekten, den Bienen, Ameisen und Termiten, an. Diese Arbeiter entwickeln sich nicht aus besonderen Eiern, sondern aus denselben, aus denen auch die fruchtbaren Individuen ihren Ursprung nehmen. Werden weibliche Larven dieser Tiere sehr reichlich und nahrhaft gefüttert, so legen sie Eier, aus denen Königinnen oder Männchen hervorgehen. Ist die Fütterung weniger ausgiebig, so bilden sich unfruchtbare Arbeiter. Es liegt nun nahe, die Ursache der Unfruchtbarkeit einfach in der minderwertigen Ernährung zu suchen. Diese Ansicht vertritt unter anderen Herbert Spencer, der englische Denker, der auf der Grundlage der natürlichen Entwickelungsgeschichte eine philosophische Weltanschauung aufgebaut hat. Weismann hält diese Ansicht nicht für richtig. Denn bei der Arbeitsbiene bleiben die Fortpflanzungsorgane nicht etwa nur in ihrer Entwickelung zurück, sondern sie werden rudimentär, sie haben einen großen Teil der für die Fortpflanzung norwendigen Teile nicht. Nun könne man aber bei anderen Insekten nachweisen, daß schlechte Ernährung durchaus keine solche Organverkümmerung nach sich zieht. Die Fliegen sind den Bienen verwandte Insekten. Weismann hat die von einem Weibchen der Schmeißfliege gelegten Eier in zwei Partien getrennt aufgezogen und die einen reichlich, die anderen spärlich gefüttert. Die letzteren wuchsen langsam und blieben auffallend klein. Aber sie pflanzten sich fort. Daraus geht hervor, daß bei den Fliegen schlechte Ernährung nicht das Unfruchtbarwerden bewirkt. Dann kann aber auch bei dem Ut-Insekt, der gemeinsamen Stammform, die man im Sinne der Entwickelungslehre für die verwandten Arten der Bienen und Fliegen annehmen muß, die Eigentümlichkeit noch nicht bestanden haben, durch schwache Ernährung unfruchtbar zu werden. Sondern es muß diese Unfruchtbarkeit eine erworbene Eigenschaft der Biene sein. Zugleich kann aber auch von einer Vererbung dieser Eigenschaft nicht die Rede sein, denn die Arbeiterinnen, die sie erworben haben, pflanzen sich nicht fort, können demnach auch nichts vererben. Es muß also im Bienenkeim selbst die Ursache dafür gesucht werden, daß sich einmal Königinnen, das andere Mal Arbeiter entwickeln. Der äußere Einfluß der schwachen Fütterung kann nichts bewirken, weil er sich nicht vererbt. Er kann nur als Reiz wirken, der die vorgebildete Keimanlage zur Entfaltung bringt. Durch Verallgemeinerung dieser und ähnlicher Ergebnisse kommt Weismann zu dem Schluß: «Die äußere Einwirkung ist niemals die wirkliche Ursache der Verschiedenheit, sondern sie spielt nur die Rolle des Reizes, der darüber entscheidet, welche der vorhandenen Anlagen zur Entwicklung gelangen soll. Die wirkliche Ursache aber liegt immer in vorgebildeten Veränderungen der Anlagen des Körpers selbst, und diese — da sie stets zweckmäßige sind — können in ihrer Entstehung nur auf Selektionsprozesse bezogen werden», auf die Auswahl der Tüchtigsten im Kampf ums Dasein. Der Kampf ums Dasein (die Selektion) «allein ist das leitende und führende Prinzip bei der Entwicklung der Organismenwelt». Derselben Ansicht wie Weismann von der Nichtvererbung erworbener Eigenschaften und der Allmacht der Selektion huldigen auch die englischen Forscher Francis Galton und Alfred Russell Wallace.
[ 47 ] Die Tatsachen, welche diese Forscher vorbringen, bedürfen gewiß der Aufklärung. Sie können eine solche aber nicht in der von Weismann angegebenen Richtung erfahren, wenn man nicht die ganze monistische Entwickelungslehre preisgeben will. Zu einem solchen Schritte können aber am wenigsten die Einwände gegen die Vererbung erworbener Eigenschaften zwingen. Denn man braucht nur die Entwickelung der Instinkte bei den höheren Tieren zu betrachten, um sich davon zu überzeugen, daß eine solche Vererbung stattfindet. Blicken wir zum Beispiel auf die Entwickelung unserer Haustiere. Manche von ihnen haben sich infolge des Zusammenlebens mit den Menschen geistige Fähigkeiten angeeignet, von denen bei ihren wilden Vorfahren nicht die Rede sein kann. Diese Fähigkeiten können doch gewiß nicht aus einer inneren Anlage stammen. Denn der menschliche Einfluß, die Erziehung, tritt als ein völlig Äußeres an diese Tiere heran. Wie sollte eine innere Anlage gerade einer bestimmten willkürlichen Einwirkung des Menschen entgegenkommen? Und dennoch wird die Dressur zum Instinkt, und dieser vererbt sich auf die Nachkommen. Ein solches Beispiel ist unwiderleglich. Von seiner Art können unzählige gefunden werden. Die Tatsache der Vererbung von erworbenen Eigenschaften besteht also, und es ist zu hoffen, daß weitere Forschungen die ihr scheinbar widersprechenden Erfahrungen Weismanns und seiner Anhänger mit dem Monismus in Einklang bringen werden.
[ 48 ] Weismann ist im Grunde doch nur auf halbem Wege zum Dualismus stehengeblieben. Seine inneren Entwickelungs-Ursachen haben nur einen Sinn, wenn sie als ideelle gefaßt werden. Denn wären sie stoffliche Vorgänge im Keimplasma, so wäre nicht einzusehen, warum diese stofflichen Vorgänge und nicht die des äußeren Geschehens im Prozeß der Vererbung fortwirken sollten. Konsequenter als Weismann ist ein anderer Naturforscher der Gegenwart, nämlich J. Reinke, der mit seinem vor kurzem erschienenen Buch: «Die Welt als Tat; Umrisse einer Weltansicht auf naturwissenschaftlicher Grundlage» den Sprung ins dualistische Lager ohne Rückhalt gemacht hat. Er erklärt, daß aus den physischen und chemischen Kräften der organischen Substanzen niemals sich ein Lebewesen aufbauen könne. «Das Leben besteht nicht in chemischen Eigenschaften einer besonderen Verbindung oder einer Mehrzahl von Verbindungen. Wie aus den Eigenschaften von Messing und Glas sich noch nicht die Möglichkeit der Entstehung des Mikroskops ergibt, so wenig folgt aus den Eigenschaften der Eiweißstoffe, Kohlehydrate, Fette, des Lecithins, Cholesterins und so weiter die Möglichkeit der Entstehung einer Zelle» (S.178 des genannten Werkes). Es müssen neben den stofflichen Kräften noch geistige oder Kräfte zweiter Hand vorhanden sein, welche den ersteren ihre Richtung geben, ihr Zusammenwirken so regeln, daß sich der Organismus ergibt. Diese Kräfte zweiter Hand nennt Reinke Dominanten. «In der Verbindung der Dominanten mit den Energien» — den Leistungen der physikalischen und chemischen Kräfte — «enthüllt sich uns eine Durchgeistigung der Natur; in dieser Auffassung gipfelt mein naturwissenschaftliches Glaubensbekenntnis» (S. 455). Es ist nun nur folgerichtig, daß Reinke auch eine allgemeine Weltvernunft annimmt, welche ursprünglich die nur chemischen und physikalischen Kräfte in den Zusammenhang gebracht hat, in dem sie in den organischen Wesen tätig sind.
[ 49 ] Dem Vorwurf, daß durch eine solche von außen auf die stofflichen Kräfte wirkende Vernunft die im Reich des Unorganischen geltende Gesetzmäßigkeit für die organische Welt außer Kraft gesetzt wird, sucht Reinke dadurch zu entgehen, daß er sagt: Die allgemeine Weltvernunft ebenso wie die Dominanten bedienen sich der mechanischen Kräfte, sie verwirklichen ihre Schöpfungen nur mit Hilfe dieser Kräfte. Das Verhalten der Weltvernunft stimmt mit dem eines Mechanikers überein, der auch die Naturkräfte arbeiten läßt, nachdem er ihnen die Richtung angewiesen hat. Mit diesem Ausspruche wird aber wieder im Sinne Eduard von Hartmanns die Art der Gesetzmäßigkeit, die sich in den mechanischen Tatsachen ausspricht, zum Handlanger einer höheren, geistigen erklärt.
[ 50 ] Goettes Formgesetz, Weismanns innere Entwickelungsursachen, Reinkes Dominanten sind eben im Grunde doch nichts anderes als Abkömmlinge der Gedanken des planmäßig bauenden Weltschöpfers. Sobald man die klare und einfache Erklärungsweise der monistischen Weltansicht verläßt, verfällt man unbedingt mehr oder weniger in mystisch-religiöse Vorstellungen, und von solchen gilt Haeckels Satz, daß «es dann besser ist, die mysteriöse Schöpfung der einzelnen Arten anzunehmen».
[ 51 ] Neben denjenigen Gegnern des Monismus, welche der Ansicht sind, daß die Betrachtung der Welterscheinungen zu geistigen Wesenheiten hinführe, die unabhängig von den stofflichen Erscheinungen sind, gibt es noch andere,9Hier konnte nur von solchen Einwänden gegen Haeckels Lehre gesprochen werden, die gewissermaßen typisch sind und die ihren Grund in veralteten, aber noch immer einflußreichen Gedankenkreisen haben. Die zahlreichen «Widerlegungen» Haekkels, die sich nur als Abarten der verzeichneten Haupteinwände darstellen, mußten ebenso unberücksichtigt bleiben wie diejenigen, die Haeckel selbst am besten in seinem Buche über «Die Welträtsel» abgetan hat, indem er den wackern Kämpfern sagt: «Erwerber Euch durch fünfjähriges fleißiges Studium der Naturwissenschaft und besonders der Anthropologie (speziell der Anatomie und Physiologie des Gehirns!) diejenigen unentbehrlichen empirischen Vorkenntnisse der fundamentalen Tatsachen, die Euch noch gänzlich fehlen.» (1. Aufl., S. 444.) die das Gebiet einer über der natürlichen schwebenden übernatürlichen Weltordnung dadurch retten wollen, daß sie dem menschlichen Erkenntnisvermögen überhaupt die Fähigkeit absprechen, die letzten Gründe des Weltgeschehens zu begreifen.10Auf welchem Mißverständnis die Annahme von Erkenntnisgrenzen beruht, habe ich nachgewiesen in meiner «Philosophie der Freiheit». Die Vorstellungen dieser Gegner haben ihren beredtesten Anwalt in Du Bois-Reymond gefunden. Seine auf der fünfundvierzigsten Versammlung deutscher Naturforscher und Ärzte (1872) gehaltene berühmte «IgnorabimusRede» ist der Ausdruck ihres Glaubensbekenntnisses. Du BoisReymond bezeichnet in dieser Rede als das höchste Ziel des Naturforschers die Erklärung aller Weltvorgänge, also auch des menschlichen Denkens und Empfindens, durch mechanische Prozesse. Gelingt es uns dereinst zu sagen, wie die Teile unseres Gehirnes liegen und sich bewegen, wenn wir einen bestimmten Gedanken oder eine Empfindung haben, so ist das Ziel der Naturerklärung erreicht. Weiter können wir nicht kommen. Damit haben wir aber nach Du Bois-Reymonds Ansicht nicht begriffen, worin das Wesen unseres Geistes besteht. «Es scheint zwar bei oberflächlicher Betrachtung, als könnten durch die Kenntnis der materiellen Vorgänge im Gehirn gewisse geistige Vorgänge und Anlagen uns verständlich werden. Ich rechne dahin das Gedächtnis, den Fluß und die Assoziation der Vorstellungen, die Folgen der Übung, die spezifischen Talente und dergleichen mehr. Das geringste Nachdenken lehrt, daß dies Täuschung ist. Nur über gewisse innere Bedingungen des Geisteslebens, welche mit den äußeren durch die Sinneseindrücke gesetzten etwa gleichbedeutend sind, würden wir unterrichtet sein, nicht über das Zustandekommen des Geisteslebens durch diese Bedingungen. — Welche denkbare Verbindung besteht zwischen bestimmten Bewegungen bestimmter Atome in meinem Gehirn einerseits, andererseits den für mich ursprünglichen, nicht weiter definierbaren, nicht wegzuleugnenden Tatsachen: «Ich fühle Schmerz, fühle Lust; ich schmecke Süßes, rieche Rosenduft, höre Orgelton, sehe Rob, und der ebenso unmittelbar daraus fließenden Gewißheit: «Also bin ich!»? Es ist eben durch. aus und für immer unbegreiflich, daß es einer Anzahl von Kohlenstoff-, Wasserstoff-, Stickstoff-, Sauerstoff- usw. Atomen nicht sollte gleichgültig sein, wie sie liegen und sich bewegen, wie sie lagen und sich bewegten, wie sie liegen und sich bewegen werden.» (S.35f.) Wer aber heißt Du Bois-Reymond erst aus der Materie den Geist auszutreiben, um nachher konstatieren zu können, daß er nicht in ihr ist! Die einfache Anziehung und Abstoßung des kleinsten Stoffteilchens ist Kraft, also eine von dem Stoff ausgehende geistige Ursache. Aus den einfachsten Kräften sehen wir in einer Stufenfolge von Entwickelungen sich den komplizierten Menschengeist aufbauen. Wir begreifen ihn aus diesem seinem Werden. «Das Problem von der Entstehung und dem Wesen des Bewußtseins ist nur ein spezieller Fall von dem generellen Hauptproblem: vom Zusammenhang von Materie und Kraft.» (Haeckel, Freie Wissenschaft und freie Lehre. S.80.) Die Frage ist eben gar nicht: wie entsteht der Geist aus der geistlosen Materie, sondern: wie entwickelt sich der kompliziertere Geist aus den einfachsten geistigen Leistungen des Stoffes: aus der Anziehung und Abstoßung? In der Vorrede, die Du Bois-Reymond zu dem Abdruck seiner «Ignorabimus-Rede» geschrieben hat, empfiehlt er denjenigen, die nicht zufrieden sind mit seiner Erklärung von der Unerkennbarkeit der tiefsten Gründe des Seins, daß sie es doch mit den Glaubensvorstellungen der übernatürlichen Weltanschauung versuchen mögen. «Mögen sie es doch mit dem einzigen anderen Ausweg versuchen, dem des Supranaturalismus. Nur daß, wo Supranaturalismus anfängt, Wissenschaft aufhört.» Aber ein solches Bekenntnis, wie das Du Bois-Reymonds, wird immer dem Supranaturalismus Tür und Tor öffnen. Denn, wo man dem menschlichen Geiste sein Wissen begrenzt, wird er seinen Glauben an Nicht-mehr-Wißbares beginnen lassen.
[ 52 ] Es gibt nur eine Rettung aus dem Glauben an eine übernatürliche Weltordnung, und das ist die monistische Erkenntnis, daß alle Erklärungsgründe für die Welterscheinungen auch innerhalb des Gebietes dieser Erscheinungen liegen. Diese Erkenntnis kann nur eine Philosophie liefern, die im innigsten Einklange mit der modernen Entwickelungslehre steht.
Haeckel and his opponents
Preface
[ 1 ] I am convinced that my "Philosophy of Freedom", published five years ago, presents a view of the world that is in full harmony with the tremendous results of the natural sciences of our time. I am aware that I did not deliberately bring about this harmony. My path was completely independent of the one taken by natural science.
[ 2 ] From this independence of my way of thinking from the prevailing field of knowledge of our day and from the simultaneous complete agreement with it, I believe I may derive the right to represent the position of the most monumental representative of the scientific way of thinking, Ernst Haeckel, within the intellectual struggle of our time.
[ 3 ] The need to engage with the natural sciences is undoubtedly felt by many today. It can best be satisfied by immersing oneself in the ideas of the natural scientist who has drawn the most unreserved conclusions from scientific premises. I would like to address this pamphlet to those who feel the same need as I do in this respect.
Berlin, January 1900.
[ 4 ] In his book on Winckelmann, Goethe gave a wonderful expression to the feeling that man has when he considers his position within the world: "When the healthy nature of man acts as a whole, when he feels himself in the world as in a great, beautiful, worthy and valuable whole, when the harmonious pleasure grants him a pure, free delight: then the universe, if it could feel itself as having reached its goal, would exult and admire the summit of its own becoming and being. " This feeling gives rise to the most meaningful question that man can ask himself: How is his own becoming and being linked to that of the whole universe? In a letter to Goethe on August 23, 1794, Schiller aptly described the path by which Goethe wanted to gain knowledge of human nature. "From the simple organization you ascend, step by step, to the more intricate ones, in order finally to build the most intricate of all, man, genetically from the materials of the whole edifice of nature." This path of Goethe's is now also the one that natural science has been following for four decades in order to solve the "question of all questions for mankind". Huxley sees it as determining the position that "man occupies in nature, and his relations to the totality of things". It is to Charles Darwin's great credit that he created a new scientific basis for thinking about this question. The facts that he communicated in 1859 in his work "On the Origin of Species" and the principles that he developed offered natural science the opportunity to show in its own way how well-founded Goethe's conviction was that nature "after a thousand and one animals, forms one being which contains them all: man". Today we can look back on forty years of scientific development under the influence of Darwin's ideas. In his essay "On our present knowledge of the origin of man", which reproduces a lecture he gave at the Fourth International Zoological Congress in Cambridge on August 26, 1898, Ernst Haeckel was right to say: "Forty years of Darwinism! What a tremendous advance in our knowledge of nature! And what a change in our most important views, not only in the areas of biology as a whole, but also in anthropology and all the so-called humanities! " From his deep knowledge of nature, Goethe foresaw this change and fully recognized its significance for the progress of human intellectual culture. We can see this particularly clearly from a conversation he had with Soret on August 2, 1830. At that time, news of the July Revolution had reached Weimar and caused an uproar. When Soret visited Goethe, he was greeted with the words: "Well, what do you think of this great event? The volcano has erupted; everything is in flames, and it is no longer a closed-door negotiation!" Of course, Soret could only believe that Goethe was talking about the July Revolution, and replied that, given the known circumstances, nothing else was to be expected than that it would end with the expulsion of the royal family. Goethe, however, had something quite different in mind. "I'm not talking about those people at all; I'm talking about quite different things. I'm talking about the dispute between Cuvier and Geoffroy de Saint-Hilaire, which broke out in public at the Academy and was so important for science!" The dispute concerned the question of whether each of the species in which organic nature expresses itself has its own particular blueprint or whether they all have one in common. Goethe had already decided this question for himself more than forty years earlier. His diligent study of the plant and animal world had made him an opponent of Linné's view that we "count as many species as different forms have been created in principle". Anyone who holds such an opinion can only endeavour to investigate the organizational plans of the individual species. Above all, he will seek to distinguish these individual forms carefully. Goethe took a different path. "That which Linné sought to keep apart by force must, according to the innermost need of my being, strive to unite." He formed the opinion that he summarized in 1796 in the "Lectures on the first three chapters of the draft of a general introduction to comparative anatomy" in the sentence: "This, then, we would have gained, to be allowed to assert unabashedly that all perfect organic natures, among which we see fishes, amphibians, birds, mammals, and at the head of the last, man, are all formed after one archetype, which only in its very constant parts deviates more or less to and fro, and still daily develops and transforms itself by reproduction. " Goethe described the archetype to which all diverse plant forms can be traced back in 1790 in his "Attempt to explain the metamorphosis of plants". This approach, through which Goethe endeavoured to recognize the laws of living nature, is very similar to the one he demands for the inanimate world in his essay "The Experiment as Mediator of Object and Subject", written in 1793: "Nothing happens in living nature that does not stand in a connection with the whole, and if the experiences only appear to us in isolation, if we have to regard the experiments only as isolated facts, it is not thereby said that they are isolated; it is only the question: how do we find the connection between these phenomena, these occurrences? " Even the species appear to us only in isolation. Goethe seeks their connection. From this it is clear that Goethe's striving is directed towards applying the same kind of explanation to the consideration of living beings that leads to the goal with inanimate nature.1Goethe and Kant. I have characterized the contrast that exists between Goethe's and Kant's world view in the introductions to my edition of Goethe's scientific writings (in Kürschner "Deutsche National-Literatur") and in my book "Goethes Weltanschauung" ("Die Metamorphose der Welterscheinungen"). It is also evident in the position of the two personalities with regard to the explanation of organic nature. Goethe seeks this explanation in the same way as modern natural science. Kant considers such an explanation impossible. Only those who delve into the essence of Goethe's world view can come to a correct judgment about its position in relation to Kant's philosophy. Goethe's own testimonies are not authoritative, as he never engaged in a more detailed study of Kant. "It was the entrance (to the Critique of Pure Reason) that appealed to me, but I could not venture into the labyrinth itself: sometimes the gift of poetry hindered me, sometimes common sense, and I felt nowhere improved." He liked individual passages in Kant's "Critique of Judgment" because he reinterpreted their meaning in such a way that it corresponded to his own world view. It is therefore only too understandable that his conversations with Kantians turned out to be strange. "They heard me well, but could neither answer me nor be of any help. More than once I encountered one or the other admitting with smiling astonishment that it was, of course, an analog of Kant's way of thinking, but a strange one." In his essay "Goethe's relationship to Kant in his historical development" (Kantstudien I, II), Karl Vorländer judged this relationship according to the wording of Goethe's self-testimonies and accused me of my view being "in contradiction with Goethe's clear self-testimonies" and at least "strongly one-sided". I would have left this objection unanswered, because I saw from Mr. Karl Vorländer's remarks that they originated from a man for whom it is quite impossible to understand a way of thinking that is foreign to him; however, it seemed necessary to me not to leave a remark linked to it without an answer. For Mr. Vorländer is one of those people who regard their opinion as absolutely correct, i.e. as stemming from the highest possible insight, and stamp any other opinion as a product of ignorance. Because I think differently about Kant than he does, he gives me the wise advice to study certain passages in Kant's works. This kind of criticism of other people's opinions cannot be rejected strongly enough. Who gives someone the right not to criticize me for a view that differs from his own, but to lecture me? I therefore told Mr. Karl Vorländer my opinion of this schoolmasterly attitude in the 4th volume of my edition of Goethe's scientific writings. He then discussed my book "Goethes Weltanschauung" in the third volume of "Kantstudien" in a way that not only surpasses the form of what he had previously done against me, but is also full of objective falsehoods. He speaks of an "isolated and embittered opposition" in which I find myself against the whole of modern philosophy (excluding Nietzsche, of course) and natural science. That's three objective untruths. Anyone who reads my writings - and anyone who judges me as Mr. Vorländer does should read them - will see that I do indeed criticize individual views of modern natural science objectively and seek to deepen others philosophically, but that to speak of a bitter opposition is downright absurd. In my "Philosophy of Freedom" I have expressed my conviction that in my views the philosophical conclusion of the edifice that "Darwin and Haeckel have erected for natural science" is given (XI. "The Moral Imagination"). The Frenchman Henri Lichtenberger, who says in his book "La philosophie de Nietzsche": "R. Steiner est l'auteur de Wahrheit und Wissenschaft et Die Philosophie der Freiheit; dans ce dernier ouvrage il complète la théorie de Nietzsche sur un point important", knows that it is I who has sharply emphasized the fundamental flaw in Nietzsche's world of ideas. He emphasizes that I have shown that Nietzsche's "Übermensch" in particular is not what it should be. The German philosopher Karl Vorländer has either not read my writings and nevertheless passes judgment on me, or he has done so and writes down the above and similar objective falsehoods. I leave it to the discerning public to decide whether his contribution, which has been deemed worthy of inclusion in a serious philosophical journal, is proof of his complete lack of judgment or a questionable contribution to German scholarly morality. How far ahead of his time he was with such ideas becomes clear when one considers that at the same time as Goethe published his Metamorphoses, Kant, in his Critique of Judgment, wanted to scientifically demonstrate the impossibility of explaining the living according to the same principles that apply to the inanimate. He asserts: "For it is quite certain that we cannot even adequately know, much less explain, organized beings and their inner possibility according to merely mechanical principles of nature; and so certain, indeed, that one can boldly say that it is unrighteous for man to grasp even such a proposition or to hope that a Newton might yet arise who would make even the production of a blade of grass comprehensible according to laws of nature which no intention has ordered; but one must deny this insight to man per se. " Haeckel rejects this idea with the words: "But now this impossible Newton really appeared seventy years later in Darwin and... and actually solved the problem that Kant considered absolutely unsolvable! " Goethe knew that the change in scientific views brought about by Darwinism would have to occur because it corresponded to his own way of thinking. In the view defended by Geoffroy de Saint-Hilaire against Cuvier, that all organic forms carry within them a "general plan, modified only here and there", he recognized his own. He was therefore able to say to Soret: "Now Geoffroy de Saint-Hilaire is also firmly on our side, and with him all his important students and followers in France. This event is of incredible value to me, and I rightly rejoice at the general victory finally achieved for a cause to which I have dedicated my life and which is also very much my own." Darwin's discoveries were of even greater value to Goethe's view of nature. Goethe's view of nature relates to Darwinism in much the same way as Copernicus' and Kepler's insights into the structure and movements of the planetary system relate to Newton's discovery of the law of the general attraction of all celestial bodies. This law shows the natural scientific reasons why the planets move in the way described by Copernicus and Kepler. And Darwin found the natural causes why the common archetype of all organic beings assumed by Goethe appears in the diverse species.
[ 5 ] Doubt about the view that every single organic species is based on a special organizational plan that is unchangeable for all time became firmly established in Darwin during a voyage he undertook as a naturalist on the ship "Beagle" to South America and Australia in the summer of 1831. We get an idea of how his thoughts matured when we read messages from him such as this: "When, during the voyage of the Beagle, I visited the Galapagos Archipelago, which lies in the Pacific Ocean about five hundred English miles from the coast of South America, I found myself surrounded by peculiar species of birds, reptiles and plants which exist nowhere else in the world. Yet almost all of them had an American flavor. In the song of the mocking-bird, in the harsh cry of the vulture, in the large lantern-like opuntia, I clearly perceived the neighborhood with America; and yet these islands were separated from the mainland by so many miles of ocean, and differed widely from it in their geological constitution and in their climate. Even more surprising was the fact that most of the inhabitants of each island of this small archipelago were specifically different, though closely related to each other... I often wondered at the time how these many peculiar plants and animals had evolved. The simplest answer seemed to be that the inhabitants of the various islands were descended from each other and had undergone modifications in the course of their descent, and that all the inhabitants of the archipelago were descended from those of the nearest mainland, namely America, from which colonization would naturally have originated. But for a long time it remained an inexplicable problem to me: how the necessary degree of modification could have been achieved." Darwin was enlightened about this how by the numerous breeding experiments he carried out with pigeons, chickens, dogs, rabbits and cultivated plants after his return home. From them he saw the extent to which organic forms are capable of continually changing in the course of their reproduction. By creating artificial conditions, it is possible to obtain new species from a certain form after a few generations, which differ much more from each other than those in the wild, whose diversity is considered so great that one would like to base a special organizational plan on each one. As is well known, the breeder uses this variability of species to develop forms of cultivated organisms that correspond to certain intentions. He seeks to create the conditions that direct the change in a direction that suits him. If he wants to breed a type of sheep with particularly fine wool, he selects those individuals within his flock of sheep that have the finest wool. He allows these to reproduce. From their offspring, he again selects those with the finest wool for further reproduction. If this is continued through a series of generations, a species of sheep is obtained which differs considerably from its ancestors in the formation of its wool. The same can be done with other characteristics of living beings. Two things emerge from these facts: that organic forms have a tendency to change, and that they inherit the assumed changes to their descendants. Through the first property of living beings, the breeder is able to develop certain characteristics in his species that suit his purposes; through the second, these new characteristics are transmitted from one generation to the next.
[ 6 ] The idea now suggests itself that forms are also constantly changing in the wild. And the great ability of cultivated organisms to change does not compel us to assume that this property of organic forms is enclosed within certain limits. On the contrary, we can assume that in the course of great periods of time a certain form transforms itself into a completely different one, which in its formation deviates from the first in the greatest conceivable way. The most natural conclusion is then that the organic species did not develop independently of each other according to a special construction plan, but that in the course of time one form develops from the other. This idea is supported by Lyell's findings on the history of the earth's development, which he first published in 1830 in his "Principles of geology". These principles did away with the older geological views according to which the formation of the earth was supposed to have taken place in a series of violent catastrophes. This theory of catastrophes was intended to explain the results of the study of the earth's solid crust. The various layers of the earth's crust and the fossilized organic beings they contain are, after all, the remnants of what has taken place on the earth's surface over the course of time. The followers of the violent upheaval doctrine believed that the development of the earth took place in successive, precisely differentiated periods. At the end of one such period a catastrophe occurred. All living things were destroyed and their remains preserved in a layer of earth. A completely new world arose above what had been destroyed and had to be recreated. Lyell replaced this theory of catastrophes with the view that the earth's crust was gradually formed over a very long period of time by the same processes that still take place every day on the surface of the earth. The action of the rivers, which carry mud from one place to another, the action of the glaciers, which grind away the rocks and push away blocks, and similar processes, have, in their steady, slow action, given the earth's surface its present form. This view necessarily leads to the other view that today's animal and plant forms have also gradually developed from those whose remains have been preserved in the fossils. Now it follows from the processes of artificial breeding that one form really can change into another. The only question that arises is how the conditions for this transformation are created in nature itself, which the breeder brings about by artificial means?
[ 7 ] In artificial breeding, human intelligence selects the conditions in such a way that the newly emerging forms are adapted to the purpose pursued by the breeder. However, the organic forms living in nature are also generally adapted to the conditions under which they live. Any glance at nature can teach us the truth of this fact. Animal and plant species are arranged in such a way that they can survive and reproduce in the conditions in which they live.
[ 8 ] It is precisely this expedient arrangement that has given rise to the prejudice that organic forms cannot be explained in the same way as the facts of inanimate nature. Kant states in the Critique of Judgment: "The analogy of forms, in so far as they appear to have been produced in accordance with a common archetype despite all their differences, strengthens the supposition of a real relationship between them in their production from a common archetypal mother through the gradual approximation of one animal species to another... Here the archaeologist of nature is now at liberty, from the remaining traces of her oldest revolutions, according to all the mechanism of the same known and conjectured to him, to let spring that great family of creatures (for so it would have to be conceived, if the said continuous kinship is to have a reason)... However, he must add to the end of this universal mother an organization that is purposeful for all these creatures, otherwise the purposeful form of the products of the animal and plant kingdom is not even conceivable in terms of its possibility."
[ 9 ] If organic forms are to be explained in the same way as natural science does with inorganic phenomena, it must be shown that the purposeful organization of organisms without a purpose intentionally placed in them arises just as naturally as an elastic ball rolls along according to law when it is pushed by another. Darwin fulfilled this requirement through his doctrine of natural selection. Organic forms must also transform themselves in nature in accordance with their ability to transform, as demonstrated by artificial breeding. If nothing is present which from the outset arranges the transformation in such a way that only expedient forms arise, then inexpedient or more or less expedient forms will arise indiscriminately. Now nature is tremendously wasteful in the production of its germs. So many germs are produced on our earth that a great number of worlds could be filled in a short time if they all came to development. This large number of germs is only matched by a relatively small amount of food and space. The consequence of this is a general struggle for existence among the organic beings. Only the efficient ones will be able to survive and reproduce; the inefficient ones must perish. The most efficient, however, will be those who are most appropriately adapted to the conditions of life. The absolutely unintentional and naturally necessary struggle for existence thus accomplishes the same thing that the intelligence of the breeder accomplishes with the cultivated organisms: it creates purposeful organic forms. This is, in broad outline, the meaning of Darwin's doctrine of natural selection in the struggle for existence or the theory of selection. It achieved what Kant considered impossible: to think of the purposeful form of the products of the animal and plant kingdoms according to their possibility, without attributing to the general mother an organization that is purposeful for all these creatures.
[ 10 ] Just as Newton's theory of the general attraction of celestial bodies showed why they move in the orbits determined by Copernicus and Kepler, it was now possible to explain, with the help of the theory of selection, how the development of living things takes place in nature, the course of which Goethe described in "On Morphology" with the words: "This much, however, we can say, that the creatures which gradually emerge from an almost indistinguishable relationship as plants and animals perfect themselves in two opposite directions, so that the plant finally becomes permanent and rigid in the tree, the animal glorifies itself in man to the highest mobility and freedom. " Goethe said of his process: "I do not rest until I find a concise point from which much can be derived, or rather which voluntarily produces much from itself and carries it towards me." For Ernst Haeckel, the theory of selection became the point from which he derived an entire scientific world view.
[ 11 ] At the beginning of our century, Jean Lamarck also held the view that at a certain time in the earth's development, the simplest organic organisms developed from mechanical, physical and chemical processes through primordial generation. These simplest organisms then produced more perfect ones, and these again became more highly organized up to man. "This part of the theory of evolution, which asserts the common descent of all animal and plant species from the simplest common ancestral forms, could therefore be called Lamarckism in honor of its most deserving founder." Haeckel gave a large-scale explanation of Lamarckism through Darwinism.
[ 12 ] Haeckel found the key to this explanation by seeking in the individual development of higher organisms in their ontogeny - the evidence that they are really descended from lower organisms. If one follows the development of the form of a higher organism from the first germ to the developed state, the various stages represent forms that correspond to the forms of lower organisms.2Biogenetic basic law. Haeckel proved the general validity and far-reaching significance of the biogenetic law in a series of works. The most important insights and evidence can be found in his "Biology of calcareous sponges" (1872) and in his "Studies on the theory of gastraea" (1873-84). Since then, other zoologists have developed and confirmed this theory. In his latest work "Die Welträtsel" (1899) Haeckel can say of it (p. 72): "Although the same was at first almost universally rejected, and for a decade was violently opposed by numerous authorities, it is nevertheless at present (for about fifteen years) accepted by all knowledgeable specialists." At the beginning of his individual existence, man and every other animal is a simple cell. This divides and a germinal vesicle consisting of many cells develops from it. This develops into the so-called cup-shaped germ, the two-layered gastrula, which has the shape of a cup-shaped or jug-shaped body. Now the lower plant animals (sponges, polyps and so on) remain at a stage of development throughout their lives which resembles this cup-shaped germ. Haeckel says: "This fact is of extraordinary importance. For we see that man, and every vertebrate animal in general, rapidly and temporarily passes through a two-leafed stage of development, which is preserved throughout the life of the lowest plant animals." (Anthropogeny p.175.) Such a parallelism between the developmental stages of the higher organisms and the developed lower forms can be traced throughout the entire history of individual development. Haeckel expresses this fact in the words: "The short ontogenesis or development of the individual is a rapid and contracted repetition, a compressed recapitulation of the long phylogenesis or development of the species." This sentence expresses the so-called basic biogenetic law. How do the higher organisms, in the course of their development, arrive at forms that resemble the lower ones? The natural explanation is that they have developed from these, so that each organism in its individual development shows us the successive forms that it has inherited from its lower ancestors.
[ 13 ] The simplest organism that once formed on earth transforms itself into new forms in the course of reproduction. Of these, the best adapted remain in the struggle for existence and pass on their characteristics to their offspring. All the forms and characteristics that an organism currently exhibits have developed over long periods of time through adaptation and inheritance. Heredity and adaptation are therefore the causes of the organic world of forms.
[ 14 ] Haeckel thus gave the scientific explanation of the manifold organic forms by seeking the relationship of the individual history of development (ontogeny) to the phylogeny (phylogeny).3Haeckel's latest writing. In his recently published book "Die Welträtsel, Gemeinverständliche Studien über monistische Philosophie" (Bonn, Emil Strauß, 1899), Haeckel has unreservedly "further elaborated, substantiated and supplemented the convictions" that he had already held for a lifetime in the above-mentioned writings. To those who have absorbed the scientific knowledge of our time, this work must appear as one of the most important manifestos of the end of the nineteenth century. It contains in mature form a complete confrontation of modern natural science with philosophical thought from the mind of the most ingenious, far-sighted natural scientist of our time. As a natural philosopher, he has fulfilled the human demand for knowledge that Schiller gained from the observation of Goethe's spirit: he has ascended from the simple organization, step by step, to the more intricate, in order to finally build the most intricate of all, the human being, genetically from the materials of the entire natural edifice. He set down his view in several large-scale works, in his "General Morphology of Organisms" (1866), in the "Natural History of Creation" (1868), in "Anthropogeny" (1874), in which he "undertook the first and so far only attempt to critically substantiate the zoological family tree of man in detail and to discuss the entire animal ancestry of our race... to discuss in detail". These works were supplemented in recent years (1894-1896) by his three-volume "Systematic Phylogeny".
[ 15 ] It is indicative of Haeckel's deep philosophical nature that after the publication of Darwin's "Origin of Species" (1859) he immediately recognized the full implications of the principles set out therein for the entire world view of man; and it speaks for his philosophical enthusiasm that he tirelessly and boldly fought all the prejudices that rose up against the inclusion of the new truth in the creed of the modern mind. The necessity that all modern scientific thought has to reckon with Darwinism was set out by Haeckel at the fiftieth meeting of German naturalists and physicians on September 18, 1877 in his lecture on "The present-day theory of evolution in relation to science as a whole". He gave a comprehensive "Confession of Faith of a Naturalist" on October 9, 1892 in Altenburg at the 75th anniversary of the Osterland Natural Research Society. (This speech is printed under the title "Monism as a bond between religion and science", Bonn 1892.) He recently developed the broad outlines of the answer to the "question of all questions" from the reformed theory of development and our current scientific knowledge in the above-mentioned lecture "On our current knowledge of the origin of man". Here Haeckel recently dealt with the consequence, which for every logical thinker follows without further ado from Darwinism, that man evolved from lower vertebrates, and indeed initially from true apes. But it was also this necessary conclusion that called upon all the old prejudices of theologians, philosophers and all those under their spell to fight against the theory of evolution. There is no doubt that the origin of the individual animal and plant forms would have been accepted if its acceptance had not also entailed the recognition of man's animal descent. "It remains", as Haeckel emphasized in his "Natural History of Creation", "an instructive fact that this recognition was by no means" - after the publication of Darwin's first work - "general, that on the contrary numerous critics of Darwin's first book (and among them very famous names) declared themselves in complete agreement with Darwinism, but completely rejected any application of it to man." With some semblance of justification, they referred to Darwin's book itself, in which there is not a word about this application. Because Haeckel ruthlessly drew this irrefutable conclusion, he was accused of being "more Darwinian than Darwin himself". Of course, this only lasted until 1871, when Darwin's work "The Descent of Man and Sexual Selection" was published. Here, he himself argues this conclusion with great boldness and clarity.
[ 16 ] It was correctly recognized that with this conclusion must fall an idea that is one of the most cherished in the collection of older human prejudices: that the "soul of man" should be a special being in itself, which has a completely different "higher origin" than all other natural things. The doctrine of descent must naturally lead to the view that the mental activities of man are only a special form of those physiological functions which are found in his vertebrate ancestors, and that these activities have developed from the mental activities of animals with the same necessity as the brain of man, which is the material condition of the mind, has developed from the vertebrate brain.
[ 17 ] Not only people with old beliefs, brought up by the various church religions, resisted the new confession, but also all those who have apparently freed themselves from these beliefs, but whose minds still think in terms of these ideas. In the following it will be shown that the latter type of minds includes a number of philosophers and scholars of high scientific standing who fought Haeckel and are still opponents of the views he advocated. They are joined by those who lack the ability to draw the necessary logical conclusions from a series of existing facts. I would like to present here the objections against which Haeckel had to fight his battle.
II
[ 18 ] The truth that Huxley expressed in 1863 in his "Testimonies to the Position of Man in Nature" sheds a bright light on the relationship of man to the higher vertebrates: "The critical comparison of all the organs and their modifications within the ape series leads us to one and the same result: The anatomical differences which separate man from the gorilla and chimpanzee are not so great as the differences which separate these apes from the lower apes." With the help of this fact, it is possible to determine the animal ancestry of man in the sense of Darwin's theory of descent. Humans share common ancestors with the eastern apes in an extinct ape species. By making appropriate use of the knowledge provided by comparative anatomy and physiology, individual developmental history and palaeontology, Haeckel has traced the animal ancestors of man, who are further ahead in time, via the prosimians, marsupials, prehistoric fishes up to the prehistoric intestines and the prehistoric animals consisting of only one cell. He has every right to say: Are the phenomena of man's individual development any less marvelous than the paleontological development from lower organisms? Why should man not have developed over great periods of time from unicellular primordial forms, since every individual undergoes the same development from the cell to the fully formed organism?
[ 19 ] But it is also not easy for the human mind to form natural ideas about the development of the individual organism from the germ to the formed state. We can see this in the thoughts that a natural scientist like Albrecht von Haller and a philosopher like Leibniz formed about this development. Haller was of the opinion that the germ of an organism already contains all the parts that appear during development, in a small but completely pre-formed state. Development should therefore not be the formation of something new from what already exists, but rather the unfolding of something that already exists and, because of its small size, is only hidden from view. If this view were correct, then all subsequent generations would also have to be nested in the first germ of an animal or plant form. Haller also drew this conclusion. He assumed that in the first human germ of the original mother Eve, the whole human race was already present in miniature. And Leibniz, too, can only think of the emergence of humans as an outgrowth of what already existed: "Thus I should think that the souls, which will one day be human souls, have existed in the seed like those of other species, that they have always existed in the form of organized bodies in the foreparents up to Adam, i.e. since the beginning of things."
[ 20 ] The human mind has a tendency to imagine that something that came into being already existed in some form before it came into being. The whole organism is supposed to be already hidden in the germ; the individual organic classes, orders, families, genera and species are supposed to exist as thoughts of a creator before their actual formation. But now the idea of development demands that we imagine the emergence of something new, something later, from something that already exists, something earlier. We should comprehend the that which has become from becoming. We cannot do this if we regard everything that has become as something that has always existed.
[ 21 ] The extent of the prejudices held against the idea of development was clearly demonstrated by the reception given to Caspar Friedrich Wolff's "Theoria generationis", published in 1759, by the researchers of evolution who subscribed to Haller's views. In this work it was shown that there is not yet a trace of the form of the developed organism in the human egg, but that its development consists of a chain of new formations. Wolff defended the idea of a real development, epigenesis, a becoming of something that does not yet exist, against the view of apparent development, nesting and unfolding. Haeckel says of Wolff's work that "despite its small size and cumbersome language, it is one of the most valuable writings in the entire field of biological literature...". Nevertheless, this remarkable work was initially unsuccessful. Although scientific studies flourished at that time as a result of Linné's encouragement, and although botanists and zoologists soon numbered not dozens but hundreds, no one paid any attention to Wolff's theory of generation. The few who had read it, however, considered it to be fundamentally wrong, especially Haller. Although Wolff proved the truth of epigenesis through the most precise observations and refuted the hypotheses of the preformation theory that were floating in the air, the "exact" physiologist Haller remained the most ardent supporter of the latter and rejected Wolff's correct doctrine with his dictatorial proclamation of power: "There is no becoming" (Nulla est epigenesis!). With such power, thought opposed a view of which Haeckel (in his "Anthropogeny") states: "Today we can hardly call this theory of epigenesis theory, because we have completely convinced ourselves of the correctness of the fact and can demonstrate it at any moment with the aid of the microscope."
[ 22 ] The deep-rooted prejudice against the idea of development can be taught us at any moment by the objections that our philosophical contemporaries raise against it. Otto Liebmann, who has repeatedly subjected the basic views of natural science to criticism in his "Analysis of Reality" and in "Thoughts and Facts", expresses himself about the idea of development in a strange way. He cannot deny the justification of the idea that higher organisms emerge from lower ones in view of the facts. He therefore tries to minimize the significance of this idea for the higher need for explanation. "Suppose descendant theory ... were complete, the great genealogical tree of organic natural beings were laid open before us, not as a hypothesis but as a historically established fact, what would we have then? An ancestral gallery, such as one also finds in princely castles; only not as a fragment, but as a completed totality." Thus, nothing significant should be done for the real explanation by showing how the later emerges as a new formation from the earlier. It is now interesting to see how Liebmann's presuppositions lead him back to the assumption that what emerges in the course of development already existed before its emergence. In the recently published second volume of his "Thoughts and Facts" he claims: "For us, of course, to whom the world appears in the visual form of time, the seed is there earlier than the plant, generation and conception are there earlier than the animal that arises from it, and the development of the embryo into the adult creature is a process that takes place in time and is prolonged in time. In the timeless world being, on the other hand, which does not come into being and does not pass away, but is once and for all, is unalterably preserved in the stream of events, and for which there is no future, no past, but only an eternal present, this before and after, this earlier and later, falls away completely... That which unfolds for us in the line of time as a slower or faster succession of a series of developmental phases is a fixed, undeveloped and imperishable law in the omnipresent, permanent world being." The connection between such philosophical ideas and the views of the various religious doctrines on creation is easy to see. Neither the religious doctrines nor philosophical thinkers such as Liebmann want to admit that purposefully arranged beings come into being in nature without an underlying activity or force that places the purposefulness into the beings. The narrative view follows the course of events and sees beings coming into being which have the quality of purposefulness without the purpose itself having been a determining factor in their creation. Purposefulness has come into being with them, but purpose has not played a part in this coming into being.4Those who would like to cling believingly to the existence of purpose in nature repeatedly emphasize that Darwin's views do not eliminate the idea of purpose, but use it even more by showing how the concatenation of causes and effects must necessarily lead by itself to the emergence of the purposeful. However, it is not a question of whether or not one admits the existence of purposive formations in nature, but whether one accepts or rejects that the purpose, the goal, acts as a cause in the emergence of these formations. Whoever makes this assumption represents teleology or the doctrine of purposefulness. On the other hand, he who says that purpose is in no way active in the formation of the organic world; that living beings arise according to necessary laws like inorganic phenomena, and that purposefulness is only there because the inexpedient cannot be maintained; that it is not the cause of the processes, but their consequence: he professes Darwinism. Those who, like Otto Liebmann, claim that "Charles Darwin is one of the greatest teleologists of our time" (Gedanken und Tatsachen, 1st edition, p. 113) do not take this into account. No, he is the greatest anti-teleologist, because he would show such minds as Liebmann, if they understood him, that the purposeful can be explained without presupposing the activity of acting purposes. The religious mode of conception reaches for the Creator, who has created the creatures purposefully according to the preconceived plan; Liebmann turns to a timeless world being, but he nevertheless allows the purposeful to be produced by the purpose. "The end or the purpose is here neither later nor earlier than the means, but it demands it by virtue of a timeless necessity." Liebmann is a good example of philosophers who seem to have freed themselves from beliefs, but who nevertheless think entirely in terms of such beliefs. They want to have their thoughts determined purely on the basis of rational considerations; however, they are guided by an inculcated theological prejudice.
[ 23 ] Reasonable reflection must therefore agree with Haeckel when he says: "Either the organisms have naturally evolved, and then they must all be descended from the simplest common ancestral forms - or that is not the case, the individual species of organisms have arisen independently of each other, and then they can only be supernaturally created by a miracle. Natural development or supernatural creation of species - there is a choice between these two possibilities, there is no third!" What is put forward by philosophers or natural scientists as such a third party to the natural theory of development proves on closer inspection to be nothing more than a belief in creation that more or less obscures or denies its origin.
[ 24 ] If we raise the question of the origin of species in its most important form, that of the origin of man, there are only two answers. Either a rational consciousness does not exist in any way before its actual appearance in the world, but it arises as a result of the nervous system concentrated in the brain, or an all-dominant world reason exists before all other beings and shapes the material in such a way that its image appears in man. Haeckel (in "Monism as a Link between Religion and Science") describes the development of the human spirit in the following way: "Just as our human body has developed slowly and gradually from a long series of vertebrate ancestors, the same is true of our soul; as a function of our brain it has developed gradually in interaction with this organ. What we briefly call the "human soul" is only the sum of our feelings, will and thoughts, the sum of physiological functions whose elementary organs are the microscopic ganglion cells of our brain. Comparative anatomy and ontogeny show us how the admirable structure of the latter, our human soul organ, has gradually evolved over millions of years from the brain forms of higher and lower vertebrates; comparative psychology teaches us how the soul itself - as a function of the brain - has developed hand in hand with this. The latter also shows us how a lower form of soul activity is already present in the lowest animals, in the unicellular primordial animals, infusoria and rhizopods. Every natural scientist who, like me, has observed the life activity of these unicellular protists for many years is positively convinced that they also possess a soul; this "cellular soul" also consists of a sum of sensations, ideas and volitional activities; the sensation, thinking and volition of our human soul is only gradually different." The totality of human soul activities, which finds its highest expression in the unified self-consciousness, corresponds to the complicated structure of the human brain just as the simple sensation and volition correspond to the organization of the primitive animal.5In recent times, Paul Flechsig has succeeded in demonstrating that in one part of the thinking organs of man there are intricate structures that are not present in other mammals. They apparently mediate those mental activities that distinguish humans from animals. The advances in physiology, which we owe to researchers such as Goltz, Munk, Wernicke, Edinger, Paul Flechsig and others, now enable us to assign individual mental expressions to specific parts of the brain as their particular functions. We see the mediators of four types of sensation in four areas of the gray cortical zone of the cerebral mantle: the sphere of body sensation in the parietal lobe, the sphere of smell in the frontal lobe, the sphere of vision in the occipital lobe, the sphere of hearing in the temporal lobe. Thinking, which connects and organizes the sensations, has its tools between these four "sensory foci". In discussing these recent physiological findings, Haeckel makes the following remark: "The four foci of thought, characterized by a peculiar and highly intricate nervous structure in front of the intermediate sensory foci, are the true 'organs of thought', the only real tools of our mental life" (Über unsere gegenwärtige Kenntnis vom Ursprung des Menschen).
[ 25 ] Haeckel demands of psychologists that they take such results into account in their explanations of the nature of the soul and not build up a sham science composed of fantastic metaphysics, one-sided, so-called inner observation of the processes of the soul, uncritical comparison, misunderstood perceptions and incomplete experiences from speculative aberrations and religious dogmas. The reproach made by this view of the outdated science of the soul is countered by philosophers and also by individual natural scientists with the assertion that what we summarize as spirit cannot be included in the material processes of the brain; the material processes in the sensory and mental spheres are not ideas, sensations and thoughts, but only material phenomena. We cannot get to know the nature of thoughts and sensations through external observation, but only through inner experience, through purely spiritual self-observation. Gustav Bunge, for example, states in a lecture entitled "Vitalism and Mechanism" (page 12): "In activity - that is where the riddle of life lies. But we have not drawn the concept of activity from sense perception, but from self-observation, from the observation of the will as it enters our consciousness, as it reveals itself to the inner sense." Some thinkers see the hallmark of a philosophical mind in the ability to rise to the insight that it is a reversal of the correct relationship of things to want to understand spiritual processes from material ones.
[ 26 ] Such objections point to a misunderstanding of the world view advocated by Haeckel. Anyone who is truly imbued with the meaning of this world view will never seek to explore the laws of spiritual life in any other way than through inner experience, through self-observation. The opponents of the scientific way of thinking speak as if their followers wanted to gain the truths of logic, ethics, aesthetics and so on not by observing spiritual phenomena as such, but from the results of brain anatomy. They then call the distorted image of the scientific world view created by such opponents materialism and never tire of repeating that this view must be unfruitful because it ignores the spiritual side of existence or at least belittles it at the expense of the material. Otto Liebmann, who may be mentioned here once again because his anti-scientific ideas are typical of the way of thinking of certain philosophers and laymen, remarks: "Suppose, however, that the knowledge of nature had reached its goal, it would be able to give me exactly the physical-organic reasons why I consider the proposition twice two is four to be true and assert it, why I consider the other proposition "twice two is five to be false and deny it, or why I must write these lines on paper right now, while I am caught up in the subjective belief that this is because I want to write them down because of their truth, which I assume" (Gedanken und Tatsachen). No scientific thinker will ever be of the opinion that the physical-organic reasons can provide information about what is true or false in the logical sense. The spiritual connections can only be recognized from the spiritual life. What is logically justified will always be decided by logic, what is artistically perfect will be decided by aesthetic judgment. Another question, however, is: How does logical thinking and aesthetic judgment arise as a function of the brain? This question alone is answered by comparative physiology and brain anatomy. And these show that rational consciousness does not exist in isolation and uses the human brain only to express itself through it, as the pianist plays the piano, but that our mental powers are just as much functions of the form elements of our brain as "every power is the function of a material body" (Haeckel, Anthropogeny).
[ 27 ] The essence of monism consists in the assumption that all world processes, from the simplest mechanical ones up to the highest human mental creations, develop in the same natural way and that everything that is used to explain phenomena is to be sought within the world itself. This view is opposed by dualism, which does not consider the pure laws of nature sufficient to explain phenomena, but instead resorts to a rational entity that rules over phenomena. As has been shown, natural science must reject this dualism.
[ 28 ] It is now argued on the part of philosophy that the means of natural science are not sufficient to justify a world view. From its point of view, natural science would be quite right if it explained the whole world process as a chain of causes and effects in the sense of a purely mechanical lawfulness; but behind this lawfulness is the actual cause, the general world reason, which only uses mechanical means to realize higher, purposeful connections. Thus, for example, Arthur Drews, who follows the path of Eduard von Hartmann, says: "The human work of art also comes about in a mechanical way, if one only has the external sequence of the individual moments in mind, without reflecting on the fact that behind all this is only the thought of the artist; nevertheless, one would rightly consider someone a fool who wanted to claim that the work of art was created purely mechanically. ... that which, from that lower point of view which is content with the mere contemplation of the effect, and which thus views the whole process, as it were, only from behind, presents itself as the lawful effect of a cause, the same thing, seen from the front, always proves to be the intended purpose of the means employed" (Die deutsche Spekulation seit Kant). And Eduard von Hartmann himself says of the struggle for existence, which makes it possible to explain living beings according to nature: "The struggle for existence and with it the whole natural selection for breeding is only a henchman of the idea, who must perform the lower services in the realization of that idea, namely the hewing and fitting of the stones measured and typically predetermined by the master builder according to their place in the great structure. To pass off this selection in the struggle for existence as the essentially sufficient explanatory principle of the development of the organic realm would be no different than if a day laborer, who helped to prepare the stones for the construction of Cologne Cathedral, wanted to declare himself the master builder of this work of art" (Philosophy of the Unconscious).
[ 29 ] If these ideas were justified, it would be up to philosophy to search for the artist behind the work of art. Philosophers have indeed attempted the most diverse dualistic explanations of world phenomena. They have constructed in their minds certain entities that are supposed to hover behind the phenomena, just as the artist's spirit reigns behind the work of art.
[ 30 ] All scientific considerations could not take away the conviction of man that the perceptible phenomena are directed by otherworldly beings if he were to find something within his own mind that points to such beings. What would anatomy and physiology be able to do with their explanation that the soul's activities are functions of the brain if the observation of these activities provided something that is to be regarded as a higher ground of explanation? If the philosopher were able to show us that a general world reason is revealed in human reason, then such an insight could not refute all scientific results.
[ 31 ] Nothing, however, refutes the dualistic worldview better than the observation of the human mind. If I want to explain an external process, for example the movement of an elastic ball that has been pushed by another, I cannot stop at mere observation, but I must look for the law that determines the direction of movement and speed of one ball by the direction and speed of the other. Such a law cannot be provided by mere observation, but only by the mental linking of the processes. Man thus draws from his mind the means to explain that which presents itself to him through observation. He must go beyond observation if he wants to understand it. Observation and thinking are the two sources of our knowledge of things. This applies to all things and processes, but not to the thinking consciousness itself. We cannot add anything to it through any explanation that does not already lie in observation. It provides us with the laws for everything else, and at the same time it also provides us with its own. If we want to demonstrate the correctness of a law of nature, we accomplish this by distinguishing and organizing observations and perceptions, by drawing conclusions, i.e. by forming concepts and ideas about experiences with the help of thought. Only thinking itself decides whether thinking is correct. Thus it is thinking that leads us beyond mere observation, but not beyond itself, in all world events.
[ 32 ] This fact is incompatible with the dualistic worldview. What the adherents of this world view so often emphasize, that the expressions of the thinking consciousness are accessible to us through the inner sense of self-observation, while we only understand the physical, the chemical events when we bring the facts of observation into the corresponding connections through logical, mathematical combination and so on, i.e. through the results of the spiritual scientific fields: rather, they should never admit this. For one need only draw the correct conclusion from the realization that observation turns into self-observation when we move from the natural sciences to the humanities. If natural phenomena were based on a general world reason or another spiritual primal being (for example Schopenhauer's will or Hartmann's unconscious spirit), then the thinking human spirit would also have to be created by this world being. A correspondence between the concepts and ideas that this spirit forms about phenomena and the laws of these phenomena would only be possible if the ideal world artist created the laws in the human soul according to which he had previously created the whole world. But then man would not be able to recognize his own spiritual activity through self-observation, but through observation of the primordial being from which he is formed. There would be no self-observation, but only observation of the intentions and purposes of the primordial being. Mathematics and logic, for example, should not be formed by man seeking the inner, intrinsic nature of spiritual connections, but by deriving these spiritual-scientific truths from the intentions and purposes of the eternal world reason. If human reason were only an image of an eternal one, then it could never gain its lawfulness through self-observation, but would have to explain it from eternal reason. Wherever such an explanation has been attempted, however, human reason has always simply been transferred out into the world. If the mystic believes that by immersing himself in his inner self he can rise to the contemplation of God, then in reality he sees only his own spirit, which he makes into a god, and when Eduard von Hartmann speaks of ideas that use the laws of nature as their agents to build the world, then these ideas are only his own, through which he explains the world to himself. Because observation of mental expressions is self-observation, therefore it is one's own self and not an external reason that expresses itself in the mind.
[ 33 ] However, the monistic theory of development is in full agreement with the fact of self-observation. If the human soul has developed slowly and gradually with the organs of the soul from lower states, it is self-evident that we can explain its emergence from below in terms of natural science, but that we can only gain the inner essence of what ultimately results from the complicated structure of the human brain by observing this essence itself. If spirit had always existed in a form similar to that of man and had ultimately only created its counter-image in man, then we should be able to derive the spirit of man from the All-Spirit; but if the spirit of man arose in the course of natural development as a new formation, then we understand its origin when we trace its line of ancestors; we learn the stage to which it ultimately came when we consider it ourselves.
[ 34 ] A philosophy that understands itself and is directed towards an unbiased observation of the human spirit thus provides further proof of the correctness of the monistic worldview. It is, however, completely incompatible with a dualistic natural science. (I have given a further explanation and detailed justification of a monistic philosophy, whose basic ideas I could only hint at here, in my "Philosophy of Freedom".)
[ 35 ] Whoever understands the monistic worldview correctly, all objections raised by ethics lose all meaning. Haeckel has repeatedly pointed out the unjustified nature of such objections and also pointed out how the assertion that scientific monism must lead to moral materialism is either based on a complete misjudgment of the former or amounts to a mere suspicion of the latter.
[ 36 ] Of course, monism sees human action as only one part of the general world event. 66The merit of having shown that there is no real opposition between the animal and human souls, but that in a natural series of development the mental activities of man follow those of animals as a higher form of the same, is due to George John Romanes, who in a comprehensive work: "Die geistige Entwicklung im Tierreich" (1. Volume, Leipzig 1885) and "Die geistige Entwicklung beim Menschen. Ursprung der menschlichen Fähigkeiten" (2nd volume, Leipzig 1893) showed "that the psychological barrier between animals and humans has been overcome". He makes it just as little dependent on a so-called higher moral world order as he makes natural events dependent on a supernatural order. "The mechanical or monistic philosophy maintains that everywhere in the phenomena of human life, as in those of the rest of nature, fixed and unalterable laws prevail, that everywhere there is a necessary causal connection, a causal nexus of phenomena, and that accordingly the whole world cognizable to us forms a unified whole, a "monon". It further asserts that all phenomena are produced only by mechanical causes, not by premeditated purposeful causes. There is no "free will" in the usual sense. Rather, in the light of the monistic view of the world, even those phenomena which we have become accustomed to regard as the freest and most independent, the manifestations of human will, appear to be just as subject to fixed laws as any other natural phenomenon" (Haeckel, Anthropogeny). Monistic philosophy only shows the phenomenon of free will in the right light. As a part of general world events, human will is subject to the same laws as all other natural things and processes. It is conditioned by natural law. But by denying the existence of higher, purposeful causes in natural events, the monistic view also declares the will to be independent of such a higher world order. The natural process of development leads the natural processes up to human self-consciousness. At this stage it leaves man to himself; he can now draw the impulses for his actions from his own spirit. If there were a general world reason, man could not draw his goals from himself, but only from this eternal reason. In the sense of monism, therefore, man's action is determined by causal moments; in the ethical sense it is not determined, because the whole of nature is not determined ethically, but by natural law. The preliminary stages of moral action are already present in lower organisms. "Even if the moral foundations developed much higher in humans later, their oldest, prehistoric source, as Darwin has shown, lies in the social instincts of animals" (Haeckel, Monism). The moral action of man is a product of development. The moral instinct of animals, like everything else in nature, perfects itself through heredity and adaptation until man sets himself moral purposes and goals out of his own spirit. Moral goals do not appear as predetermined by a supernatural world order, but as a new formation within the natural process. In moral terms, "only that which man has made purposeful is purposeful, for only through the realization of an idea does purposefulness arise. But the idea becomes effective in the realistic sense only in man... To the question: What is man's task in life, monism can only answer: the one he sets for himself. My mission in the world is not an (ethically) predetermined one, but the one I choose for myself. I do not set out on my life's journey with a fixed course" (see my "Philosophy of Freedom", XI: World Purpose and Life Purpose). Dualism demands submission to moral commandments taken from somewhere. Monism points man to himself. He does not receive moral standards from any external world being, but only from his own being. The ability to create ethical purposes for oneself can be called moral imagination. Through it, man elevates the ethical instincts of his lower ancestors to moral action, just as he reflects the figures and processes of nature on a higher level in his works of art through his artistic imagination.
[ 37 ] The philosophical considerations arising from the existence of self-observation are thus not a refutation, but an important addition to the evidence of the monistic worldview taken from comparative anatomy and physiology.
III
[ 38 ] The famous pathologist Rudolf Virchow 6The merit of having shown that there is no real opposition between the animal and human soul, but that in a natural series of development the mental activities of man follow those of animals as a higher form of the same, is due to George John Romanes, who in a comprehensive work: "Die geistige Entwicklung im Tierreich" (1st volume, Leipzig 1885) and "Die geistige Entwicklung beim Menschen. Ursprung der menschlichen Fähigkeiten" (2nd volume, Leipzig 1893) showed "that the psychological barrier between animals and humans has been overcome". takes a peculiar position with regard to the monistic world view. After Haeckel had given his lecture on "The present-day theory of development in relation to science as a whole" at the fiftieth meeting of German natural scientists and physicians, in which he intellectually explained the significance of the monistic world view for our intellectual culture and also for the human race, Virchow appeared four days later at the same meeting as his opponent with the speech: "The freedom of science in the modern state". At first it seemed as if Virchow only wanted monism banned from the school because, in his view, the new doctrine was merely a hypothesis and not a fact supported by reliable evidence. However, it seems strange when a modern natural scientist allegedly wants to ban the doctrine of evolution from the classroom for lack of irrefutable evidence and at the same time advocates the dogma of the Church. Virchow says (on page 29 of the aforementioned speech): "Every attempt to transform our problems into doctrines, to introduce our conjectures as the foundations of teaching, the attempt in particular to simply depossess the Church and to replace its dogma without further ado by a religion of descent, yes, gentlemen, this attempt must fail, and in its failure it will at the same time entail the greatest dangers for the position of science in general!" One must raise the question that is meaningless to any rational thinking: Is there more certain proof for the dogmas of the Church than for the "religion of descent"? From the whole way in which Virchow spoke at the time, however, it is clear that he was less concerned with averting the dangers that monism could bring to teaching than with his principled opposition to this world view in general. He has proven this by his entire behavior since then. He has seized every opportunity that seemed suitable to him to fight against the natural history of development and to repeat his favorite sentence: "It is quite certain that man does not descend from apes." At the twenty-fifth anniversary celebration of the foundation of the "German Anthropological Society" on August 24, 1894, he even dressed this sentence in the not very tasteful words: "One has arrived at the ape theory by way of speculation; one could just as well have ... to an elephant theory or a shaft theory." Of course, this statement does not make the slightest sense in the light of the results of comparative zoology. "No zoologist" - remarks Haeckel - "will consider it possible that man can descend from the elephant or the sheep. For these two mammals belong to the most specialized branches of the ungulates, an order of mammals that has no direct connection with that of the apes or primates (except for the common descent from an original phylum of the whole class)." - As difficult as it is for the meritorious natural scientist, such statements can only be described as empty phrases.7On 3. On October 3, 1898, Virchow delivered the second of the "Huxley Lectures" at Charing Cross Hospital Medical School in London, in which he said: "I may assume that I would not have been given such an assignment if the clients had not known how deep the feeling of reverence for Huxley is in my soul, if they had not seen how I had recognized his achievements from the first groundbreaking publications of the late master and how much I appreciated the friendship he personally bestowed on me." Now it was precisely these pioneering publications by Huxley that represented the first major step towards the development of the theory of the ape ancestry of man, which Virchow opposes and about which he knows nothing to say in the Huxley lecture "The Recent Advances in Science" other than a few words that are quite meaningless compared to the current state of the question, such as: "One may think what one likes about the origin of man, the conviction of the fundamental correspondence of human and animal organization is generally accepted at present ... and so on." Virchow follows a very peculiar tactic in his fight against the theory of descendants. He demands incontrovertible proof for this theory. However, as soon as natural science finds something that is able to add a new link to the chain of evidence, he seeks to invalidate its conclusiveness in every way. The Descent Theory sees in the famous skulls of Neanderthal, Spy and so on isolated paleontological remains of extinct lower human races, which form a transitional link between the ape-like ancestor of man (Pithecanthropus) and the lower human races of the present. Virchow declared these skulls to be abnormal, pathological formations, pathological products. He even developed this assertion to the effect that all deviations from the once established organic archetypes are such pathological formations. So if we produce dessert fruit from wild fruit through artificial breeding, we have only produced a diseased natural object. There is no more convenient way of proving Virchow's proposition, which is hostile to all theories of development: "The plan of organization is unchangeable within the species, species does not give rise to species", than by declaring that what is before our eyes, as species gives rise to species, is not a healthy, natural product of development, but a diseased entity. Virchow's assertions about the bone remains of the great ape (Pithecanthropus erectus), which Eugen Dubois found in Java in 1894, were entirely consistent with this attitude towards the theory of descent. However, these remains, a skullcap, a femur and some teeth, were incomplete. At the zoological congress in Leiden [1895], a highly interesting debate arose about them. Out of twelve zoologists, three were of the opinion that the remains were from an ape, three that they were from a man, and six were of the opinion that we were dealing with an 'extinct transitional form between man and ape. Dubois has explained the relationship of this intermediate link between man and ape to the lower races of the human race on the one hand, and to the known apes on the other. Virchow declared that the skull and the thigh do not belong together, but that the former originates from an ape, the latter from a human being. This assertion was refuted by expert palaeontologists who, on the basis of the conscientious report on the finds, stated that there could not be the slightest doubt about the origin of the bone remains from one and the same individual. Virchow tried to prove that the thigh could only have come from one person by showing a bone growth on it, which must have been caused by a disease that could only be cured by careful human care. The paleontologist Marsh, on the other hand, showed that similar bone growths also occur in wild apes. A third assertion by Virchow, that the deep constriction between the upper edge of the eye sockets and the lower skull roof of the Pithecanthropus speaks for its ape nature, was rejected by the palaeontologist Nehring with the fact that the same formation is found on a human skull from Santos in Brazil.
[ 39 ] Virchow's fight against the theory of evolution does indeed seem puzzling when one considers that at the beginning of his scientific career, before the publication of Darwin's "Origin of Species" in 118591, this researcher advocated the doctrine of the mechanical basis of all life activity. In Würzburg, where Virchow taught from 1848-1856, Haeckel "sat devoutly at his feet and first heard from him with enthusiasm that clear and simple doctrine". Virchow, however, opposed the theory of transformation created by Darwin, which provided a comprehensive explanatory principle for this doctrine. When he continually emphasizes the lack of "certain proofs" with regard to the facts of fossilization, comparative anatomy and physiology, it can only be argued that knowledge of the facts is not enough to recognize the theory of evolution, but that - as Haeckel says - "a philosophical understanding" of it is also necessary. It is "only through the most intimate interaction and mutual interpenetration of experience and philosophy that the unshakeable edifice of true monistic science emerges" (Haeckel, Natürliche Schöpfungsgeschichte). More dangerous than all the damage that a "religion of descent" can do to immature minds is Virchow's battle against the doctrine of descent, which has been waged for decades to the applause of theological and other reactionaries. A factual debate with Virchow is made more difficult by the fact that he basically sticks to mere denial and generally does not raise any factual objections to the doctrine of evolution.
[ 40 ] Other scientific opponents of Haeckel make it easier for us to arrive at clarity about them because they give the reasons for their opposition and we can therefore see the errors in their conclusions. They include Wilhelm His and Alexander Goette.
[ 41 ] His appeared in 1868 with his "Untersuchungen über die erste Anlage des Wirbeltierleibes". His struggle is directed above all against the doctrine that the development of the form of a higher organism from the first germ to the fully formed state is explained by the development of the stem. We are not to explain this development by representing it as the result of the development of the generations from which the individual organism descends, mediated by heredity and adaptation, but we are to seek the mechanical causes of its development in the individual organism itself, without regard to comparative anatomy and phylogeny. His assumes that the germ, conceived as a uniform surface, grows unequally in different places, and maintains that as a result of this unequal growth the complicated structure of the organism emerges in the course of development. He says: take a simple plate and imagine that it has a different drive for enlargement at different points. Then one will be able to develop from purely mathematical and mechanical laws the state in which the structure must be after some time. Its successive forms will correspond exactly to the stages of development through which the individual organism passes from the germ to the perfect state. Thus we need not go beyond the consideration of the individual organism in order to understand its development, but we can deduce it from the mechanical law of growth itself. "All formation, whether it consists in the splitting of leaves, in the formation of folds or in complete separation, arises as a consequence of this basic law." The two pairs of limbs are produced by the law of growth in the following way: "Their arrangement is determined, like the four corners of a letter, by the intersection of four folds surrounding the body." His rejects the use of phylogeny on the grounds: "If the history of development has thoroughly fulfilled the task of physiological derivation for a given form, then it can rightly say that it has explained this form as an individual form." In reality, however, such an explanation does nothing at all. For the question is: why do different growth forces act at different parts of the germ? They are simply assumed by His to be present. The explanation can only be seen in the fact that the growth conditions of the individual parts of the germ are transmitted from the ancestor animals by inheritance, that thus the individual organism passes through the successive stages of its development, because the changes that its ancestors experienced over large periods of time continue to have an effect as the cause of its individual development.
[ 42 ] The consequences of His' view are best illustrated by his "cave lobe theory". It is intended to explain the so-called "rudimentary organs" of the organism. These are parts that are present in the organism without having any significance for its life. For example, man has a fold of hair at the inner corner of his eye which is of no use whatsoever for the functions of his visual organ. He also has muscles corresponding to those by which certain animals can move their ears at will. Nevertheless, most people cannot move their ears. Some animals have eyes that are covered by skin and therefore cannot be used for seeing. His explains these organs as those to which "no physiological role has yet been assigned, ... comparable to the waste that cannot be completely avoided when cutting a dress, even when the fabric is used most sparingly". The theory of development provides the only possible explanation for them. They are inherited from the foreparents. They served a good purpose for them. Animals that live underground today and have non-seeing eyes are descended from ancestors who lived in the light and needed eyes. Over the course of many generations, the living conditions of such an organic tribe have changed. The creatures have adapted to the new conditions, in which their organs of sight are dispensable. But these have remained as heirlooms from an earlier stage of development, only they have atrophied in the course of time because they were not needed. These rudimentary organs 8About these organs Haeckel says in his book "Die Welträtsel",. 306: "All higher animals and plants, in general all those organisms whose bodies are not quite simply constructed, but are composed of several organs working together for a purpose, reveal on careful examination a number of useless or ineffective, indeed in some cases even dangerous and harmful devices.... We find the explanation of these useless devices very simply in the theory of descendency. It shows that these rudimentary organs have atrophied through disuse.... The blind struggle for existence between the organs causes their historical decline just as it originally caused their formation and development." are one of the strongest pieces of evidence for the natural theory of development. If there had been any purposeful intentions in the construction of an organic form, where would these inappropriate parts have come from? There is no other possible explanation for them than that they have gradually fallen into disuse over the course of many generations.
[ 43 ] Alexander Goette is also of the opinion that the developmental stages of the individual organism do not need to be explained in a roundabout way through phylogeny. He derives the formation of the organism from a "law of form", which must be added to the physical and chemical processes of the material in order to form the living being. He tried to defend this point of view in detail in his "Developmental History of the Toad". "The essence of development consists in the complete but very gradual introduction into the existence of certain natural bodies of a new, externally conditioned moment, namely the law of form." Since the law of form is to be added from without to the mechanical and physical properties of matter and is not to develop from these properties, it can be nothing other than an idea free of matter, and we have 'given nothing in it which essentially differs from the ideas of creation which, according to the dualistic world-view, underlie organic forms. It is supposed to be a motive existing apart from organized matter and causing its development. In other words, it makes use of the laws of matter just as much as Eduard von Hartmann's idea. Goette must invoke this "law of form" because he is of the opinion that "the individual developmental history of organisms" alone justifies and explains their entire formation. Whoever denies that the true causes of the development of the individual being are a historical result of ancestral development will necessarily have to resort to such ideal causes lying outside the substance,
[ 44 ] A weighty testimony against such attempts to introduce ideal formative forces into the history of individual development is provided by the achievements of those naturalists who have really explained the forms of higher living beings on the assumption that these forms are the hereditary repetition of countless phylogenetic changes that have taken place over long periods of time. A striking example in this respect is the "vertebral theory of cranial bones", which had already been anticipated by Goethe and Oken, but which was only put into perspective by Carl Gegenbaur on the basis of the theory of descent. He proved that the skulls of the higher vertebrates and also of humans were formed by the gradual transformation of a primordial skull, the shape of which is still preserved today by the primordial fishes or selachians in their head formation. Based on such results, Gegenbaur rightly remarks: "Comparative anatomy will also provide a touchstone for the theory of descendants. So far there is no comparative anatomical experience that would contradict it; on the contrary, they all lead us to it. Thus this theory will receive back from science what it has given to its method: clarity and certainty" (see the introduction to Gegenbaur's "Comparative Anatomy"). The theory of descent has pointed science towards seeking the real causes of the individual development of the individual organism in its ancestors, and in this way natural science replaces all ideal laws of development, which are supposed to approach the organic substance from somewhere outside, with the actual processes of phylogeny, which continue to work in the individual being as formative forces.
[ 45 ] Under the influence of the theory of descent, natural science is increasingly approaching the great goal that one of the greatest natural scientists of the century, Karl Ernst von Baer, outlined with the words: "It is a basic idea that runs through all forms and stages of animal development and governs all individual relationships. It is the same basic idea that gathered the distributed masses in space into spheres and connected them into solar systems; the same idea that caused the weathered dust on the surface of the planet to grow into living forms. But this thought is nothing but life itself, and the words and syllables in which it expresses itself are the various forms of the living." Another of Baer's sayings gives the same idea in a different form: "Many a prize will still be awarded. The palm tree, however, will be won by the fortunate one to whom it is reserved to lead the formative forces of the animal body back to the general forces or life-directions of the world as a whole."
[ 46 ] It is the same general forces of nature that roll down the stone on an inclined plane and that also give rise to the other through the development of one organic form. The characteristics that a form acquires through generations by way of adaptation are passed on to its descendants. What a living being currently unfolds from within out of its germinal disposition has developed externally in its ancestors in a mechanical struggle with the other forces of nature. In order to maintain this view, however, it is necessary to assume that the forms acquired in this external struggle can really be inherited. For this reason, the opinion advocated by August Weismann in particular, that acquired characteristics are not inherited, calls into question the whole theory of development. He is of the opinion that no external change which has taken place in an organism can be transmitted to its descendants, but that only that which was predetermined by an original disposition of the germ is inherited. The germs of organisms are said to contain innumerable possibilities for development. Accordingly, organic forms can change in the course of their reproduction. A new form arises when the possibilities for development in the offspring are different from those of the ancestors. Of the new forms that emerge in this way, those that are best able to survive the struggle for existence will survive. Forms that are not up to this struggle will perish. If a form emerges from a developmental possibility that is particularly capable in the competitive struggle, then this form will reproduce itself; if this is not the case, it must perish. As you can see, the external causes acting on the organism are completely eliminated here. The reasons why the forms change lie in the germ. And the struggle for existence selects the most suitable forms from the most diverse germs. The characteristic of an organism does not lead us up to a change that took place with its ancestor as its cause, but to a disposition in the germ of this ancestor. Since, therefore, nothing can be brought about from without in the structure of organic forms, the germ of the original form from which a phylum has begun its development must already contain the predispositions for the following generations. We are again faced with a theory of nesting. Weismann conceives of the progressive process by which the germs bring about development as a material process. When an organism comes into being, a part of the germ mass from which it develops is merely used to form a new germ for the purpose of further reproduction. In the germ mass of an offspring there is therefore a part of that of the parents, in the germ mass of the parents a part of that of the grandparents, and so on up to the original form. An originally existing germ substance is thus preserved through all organisms that develop apart. This is Weismann's theory of the continuity and immortality of germplasm. He believes he is forced to adopt this view because numerous facts seem to contradict the assumption that acquired characteristics are inherited. One of the most remarkable is the presence of workers incapable of reproduction in the state-forming insects, bees, ants and termites. These workers do not develop from special eggs, but from the same eggs from which the fertile individuals take their origin. If female larvae of these animals are fed very abundantly and nutritiously, they lay eggs from which queens or males emerge. If the feeding is less abundant, infertile workers are formed. It is now obvious to look for the cause of infertility simply in inferior nutrition. This view is held by Herbert Spencer, the English thinker who built up a philosophical world view based on the history of natural development. Weismann does not consider this view to be correct. For in the worker bee the reproductive organs not only remain behind in their development, but they become rudimentary, they do not have a large part of the parts necessary for reproduction. However, it has been shown in other insects that poor nutrition does not lead to such organ atrophy. Flies are insects related to bees. Weismann reared the eggs laid by a female blowfly separately in two batches and fed one of them abundantly and the other sparingly. The latter grew slowly and remained remarkably small. But they reproduced. This shows that poor nutrition does not cause the flies to become infertile. But then the Ut insect, the common ancestral form that must be assumed for the related species of bees and flies according to the theory of development, cannot have had the peculiarity of becoming infertile due to poor nutrition. Rather, this infertility must be an acquired characteristic of the bee. At the same time, however, there can be no question of this trait being inherited, because the workers who have acquired it do not reproduce and therefore cannot pass it on. The reason why queens develop one time and workers another time must therefore be sought in the bee germ itself. The external influence of poor feeding cannot have any effect because it is not inherited. It can only act as a stimulus that causes the pre-formed germination system to develop. By generalizing these and similar results, Weismann comes to the conclusion: "The external influence is never the real cause of the difference, but it only plays the role of the stimulus that decides which of the existing predispositions is to develop. The real cause, however, always lies in pre-formed changes in the dispositions of the body itself, and these - since they are always purposeful - can only be related in their origin to selection processes", to the selection of the most efficient in the struggle for existence. The struggle for existence (selection) "alone is the guiding and leading principle in the development of the world of organisms". The English researchers Francis Galton and Alfred Russell Wallace subscribe to the same view as Weismann of the non-inheritance of acquired characteristics and the omnipotence of selection.
[ 47 ] The facts presented by these researchers certainly require clarification. But they cannot be clarified in the direction indicated by Weismann if one does not wish to abandon the entire monistic theory of development. But the objections to the inheritance of acquired characteristics can least of all force us to take such a step. For one need only look at the development of instincts in the higher animals to be convinced that such inheritance takes place. Let us look, for example, at the development of our domestic animals. Some of them have acquired mental faculties as a result of living together with man, which cannot be said of their wild ancestors. These abilities can certainly not come from an inner disposition. For human influence, education, comes to these animals as something completely external. How should an inner disposition be able to accommodate a certain arbitrary human influence? And yet the training becomes an instinct, and this is passed on to the offspring. Such an example is irrefutable. Countless others of its kind can be found. The fact of the inheritance of acquired characteristics therefore exists, and it is to be hoped that further research will reconcile the apparently contradictory experiences of Weismann and his followers with monism.
[ 48 ] Weismann is basically only halfway to dualism. His inner causes of development only make sense if they are understood as ideal. For if they were material processes in the germ-plasm, it would be difficult to see why these material processes and not those of external events should continue to have an effect in the process of heredity. More consistent than Weismann is another contemporary natural scientist, namely J. Reinke, who in his recently published book "Die Welt als Tat; Umrisse einer Weltansicht auf naturwissenschaftlicher Grundlage" (The World as Act; Outlines of a World View on a Scientific Basis) has made the leap into the dualistic camp without support. He explains that a living being can never be built from the physical and chemical forces of organic substances. "Life does not consist in the chemical properties of a particular compound or a plurality of compounds. Just as the properties of brass and glass do not give rise to the possibility of a microscope, the properties of proteins, carbohydrates, fats, lecithin, cholesterol and so on do not give rise to the possibility of a cell" (p. 178 of the aforementioned work). In addition to the material forces, there must also be spiritual or second-hand forces that give the former their direction and regulate their interaction in such a way that the organism results. Reinke calls these second-hand forces dominants. "In the connection of the dominants with the energies" - the achievements of the physical and chemical forces - "a spiritualization of nature is revealed to us; my scientific creed culminates in this view" (p. 455). It is now only logical that Reinke also assumes a general world reason, which originally brought the only chemical and physical forces into the context in which they are active in organic beings.
[ 49 ] Reinke tries to avoid the reproach that such a reason acting from outside on the material forces overrides the lawfulness for the organic world that is valid in the realm of the inorganic by saying: The general world reason as well as the dominants make use of the mechanical forces, they realize their creations only with the help of these forces. The behavior of world reason corresponds to that of a mechanic, who also lets the forces of nature work after he has given them direction. With this statement, however, in the sense of Eduard von Hartmann, the kind of lawfulness that expresses itself in the mechanical facts is again declared to be the handmaiden of a higher, spiritual one.
[ 50 ] Goette's law of form, Weismann's inner causes of development, Reinke's dominants are basically nothing other than descendants of the thoughts of the creator of the world who builds according to plan. As soon as one leaves the clear and simple explanation of the monistic world view, one necessarily falls more or less into mystical-religious ideas, and of such Haeckel's sentence applies that "it is then better to assume the mysterious creation of the individual species".
[ 51 ] In addition to those opponents of monism who are of the opinion that the observation of world phenomena leads to spiritual entities that are independent of material phenomena, there are others, 9Here we could only speak of those objections to Haeckel's doctrine which are to a certain extent typical and which have their basis in outdated but still influential circles of thought. Haeckel's numerous "refutations", which are merely variants of the main objections listed, had to be disregarded, as did those that Haeckel himself dismissed best in his book on "Die Welträtsel", in which he tells the brave fighters: "Acquire through five years of diligent study of natural science and especially of anthropology (especially the anatomy and physiology of the brain!) that indispensable empirical knowledge of the fundamental facts which you still completely lack." (1st ed, p. 444.) who want to save the realm of a supernatural world order hovering above the natural one by denying the human faculty of knowledge the ability to comprehend the ultimate causes of world events. 10In my "Philosophy of Freedom" I have demonstrated the misunderstanding on which the assumption of the limits of knowledge is based. The ideas of these opponents have found their most eloquent advocate in Du Bois-Reymond. His famous "Ignorabimus speech" delivered at the forty-fifth assembly of German natural scientists and physicians (1872) is the expression of their creed. In this speech, Du Bois-Reymond describes the highest goal of the natural scientist as the explanation of all world processes, including human thought and feeling, through mechanical processes. If one day we succeed in saying how the parts of our brain are located and move when we have a certain thought or sensation, then the goal of explaining nature will have been achieved. We can go no further. In Du Bois-Reymond's view, however, we have not yet grasped the essence of our mind. "At a superficial glance, it would appear that knowledge of the material processes in the brain can help us understand certain mental processes and dispositions. I include memory, the flow and association of ideas, the consequences of exercise, specific talents and the like. The slightest reflection teaches us that this is deception. We would only be informed about certain inner conditions of mental life, which are approximately equivalent to the outer conditions set by sense impressions, not about the coming into being of mental life through these conditions. - What conceivable connection is there between certain movements of certain atoms in my brain on the one hand, and on the other the facts that are original for me, cannot be further defined, cannot be denied: "I feel pain, feel pleasure; I taste sweetness, smell the scent of roses, hear the sound of an organ, see Rob, and the certainty that flows just as directly from this: "Therefore I am!"? It is utterly and forever incomprehensible that a number of carbon, hydrogen, nitrogen, oxygen, etc. atoms should not be indifferent. atoms should not be indifferent to how they lie and move, how they lay and moved, how they will lie and move." (p.35f.) But who is Du Bois-Reymond to first drive the spirit out of matter in order to be able to state afterwards that it is not in it! The simple attraction and repulsion of the smallest particle of matter is force, i.e. a spiritual cause emanating from the matter. From the simplest forces we see the complicated human spirit building up in a gradual sequence of developments. We understand it from this process of becoming. "The problem of the origin and nature of consciousness is only a special case of the general main problem: the connection between matter and force." (Haeckel, Freie Wissenschaft und freie Lehre. p.80.) The question is not at all: how does spirit arise from spiritless matter, but: how does the more complicated spirit develop from the simplest spiritual achievements of matter: from attraction and repulsion? In the preface that Du Bois-Reymond wrote to the reprint of his "Ignorabimus speech", he recommends to those who are not satisfied with his explanation of the unknowability of the deepest causes of existence that they should try the beliefs of the supernatural world view. "Let them try the only other way out, that of supranaturalism. Except that where supranaturalism begins, science ends." But such a confession, like Du Bois-Reymond's, will always open the door to supranaturalism. For where one limits the human mind's knowledge, it will allow its belief in what is no longer knowable to begin.
[ 52 ] There is only one salvation from the belief in a supernatural world order, and that is the monistic realization that all explanatory reasons for world phenomena also lie within the realm of these phenomena. This insight can only be provided by a philosophy that is in the most intimate harmony with the modern theory of development.